diff --git a/src/main/kotlin/com/mparticle/kits/AppsFlyerKit.kt b/src/main/kotlin/com/mparticle/kits/AppsFlyerKit.kt
index 0226a0b..d4cd230 100644
--- a/src/main/kotlin/com/mparticle/kits/AppsFlyerKit.kt
+++ b/src/main/kotlin/com/mparticle/kits/AppsFlyerKit.kt
@@ -29,6 +29,7 @@ import com.mparticle.MParticle
 import com.mparticle.commerce.CommerceEvent
 import com.mparticle.commerce.Product
 import com.mparticle.consent.ConsentState
+import com.mparticle.identity.MParticleUser
 import com.mparticle.internal.Logger
 import com.mparticle.internal.MPUtility
 import org.json.JSONArray
@@ -47,7 +48,8 @@ class AppsFlyerKit :
     KitIntegration.CommerceListener,
     AppsFlyerConversionListener,
     KitIntegration.ActivityListener,
-    KitIntegration.UserAttributeListener {
+    KitIntegration.UserAttributeListener,
+    KitIntegration.IdentityListener {
     override fun getInstance(): AppsFlyerLib = AppsFlyerLib.getInstance()
 
     override fun getName() = NAME
@@ -74,6 +76,8 @@ class AppsFlyerKit :
         setIntegrationAttributes(integrationAttributes)
         AppsFlyerLib.getInstance().subscribeForDeepLink(deepLinkListener())
 
+        updateCustomerUserIDIfNeededForUser(currentUser)
+
         val messages: MutableList<ReportingMessage> = ArrayList()
         messages.add(
             ReportingMessage(
@@ -107,6 +111,7 @@ class AppsFlyerKit :
     ): List<ReportingMessage> = emptyList()
 
     override fun logEvent(event: CommerceEvent): List<ReportingMessage> {
+        val event = commerceEventWithAppsFlyerCustomerUserId(event)
         val messages: MutableList<ReportingMessage> = LinkedList()
         val eventValues: MutableMap<String, Any?> = HashMap()
         val productList = event.products
@@ -215,9 +220,13 @@ class AppsFlyerKit :
             event.productAction == Product.PURCHASE
 
     override fun logEvent(event: MPEvent): List<ReportingMessage> {
-        var hashMap: HashMap<String?, Any?>? = hashMapOf()
-        if (event.customAttributes?.isNotEmpty() == true) {
-            hashMap = event.customAttributes?.let { HashMap(it) }
+        val hashMap: HashMap<String?, Any?> =
+            event.customAttributes
+                ?.takeIf { it.isNotEmpty() }
+                ?.let { HashMap(it) }
+                ?: hashMapOf()
+        customerIdForAppsFlyer(currentUser)?.takeIf { it.isNotEmpty() }?.let { cid ->
+            hashMap[AF_CUSTOMER_USER_ID] = cid
         }
         instance.logEvent(context, event.eventName, hashMap)
         val messages: MutableList<ReportingMessage> = LinkedList()
@@ -307,7 +316,11 @@ class AppsFlyerKit :
     override fun removeUserIdentity(identityType: MParticle.IdentityType) {
         with(instance) {
             if (MParticle.IdentityType.CustomerId == identityType) {
-                setCustomerUserId("")
+                if (isUserIdentificationMPID() || isUserIdentificationCustomerId()) {
+                    updateCustomerUserIDIfNeededForUser(currentUser)
+                } else {
+                    setCustomerUserId("")
+                }
             } else if (MParticle.IdentityType.Email == identityType) {
                 setUserEmails(AppsFlyerProperties.EmailsCryptType.NONE, "")
             }
@@ -320,7 +333,9 @@ class AppsFlyerKit :
     ) {
         with(instance) {
             if (MParticle.IdentityType.CustomerId == identityType) {
-                setCustomerUserId(identity)
+                if (!isUserIdentificationMPID()) {
+                    setCustomerUserId(identity)
+                }
             } else if (MParticle.IdentityType.Email == identityType) {
                 setUserEmails(AppsFlyerProperties.EmailsCryptType.NONE, identity)
             }
@@ -329,6 +344,71 @@ class AppsFlyerKit :
 
     override fun logout(): List<ReportingMessage> = emptyList()
 
+    override fun onIdentifyCompleted(
+        mParticleUser: MParticleUser,
+        identityApiRequest: FilteredIdentityApiRequest,
+    ) {
+        updateCustomerUserIDIfNeededForUser(mParticleUser)
+    }
+
+    override fun onLoginCompleted(
+        mParticleUser: MParticleUser,
+        identityApiRequest: FilteredIdentityApiRequest,
+    ) {
+        updateCustomerUserIDIfNeededForUser(mParticleUser)
+    }
+
+    override fun onLogoutCompleted(
+        mParticleUser: MParticleUser,
+        identityApiRequest: FilteredIdentityApiRequest,
+    ) {
+        updateCustomerUserIDIfNeededForUser(mParticleUser)
+    }
+
+    override fun onModifyCompleted(
+        mParticleUser: MParticleUser,
+        identityApiRequest: FilteredIdentityApiRequest,
+    ) {
+        updateCustomerUserIDIfNeededForUser(mParticleUser)
+    }
+
+    override fun onUserIdentified(mParticleUser: MParticleUser) {
+        updateCustomerUserIDIfNeededForUser(mParticleUser)
+    }
+
+    private fun isUserIdentificationMPID(): Boolean = USER_IDENTIFICATION_MPID == settings[USER_IDENTIFICATION_TYPE]
+
+    private fun isUserIdentificationCustomerId(): Boolean = USER_IDENTIFICATION_CUSTOMER_ID == settings[USER_IDENTIFICATION_TYPE]
+
+    private fun customerIdForAppsFlyer(user: MParticleUser?): String? {
+        if (user == null) {
+            return null
+        }
+        return when {
+            isUserIdentificationMPID() -> user.id.toString()
+            isUserIdentificationCustomerId() ->
+                user.getUserIdentities()[MParticle.IdentityType.CustomerId]
+            else -> user.id.toString()
+        }
+    }
+
+    private fun updateCustomerUserIDIfNeededForUser(user: MParticleUser?) {
+        if (!isUserIdentificationMPID() && !isUserIdentificationCustomerId()) {
+            return
+        }
+        instance.setCustomerUserId(customerIdForAppsFlyer(user))
+    }
+
+    private fun commerceEventWithAppsFlyerCustomerUserId(event: CommerceEvent): CommerceEvent {
+        val cid = customerIdForAppsFlyer(currentUser)?.takeIf { it.isNotEmpty() } ?: return event
+        val newAttrs = HashMap<String, String>()
+        event.customAttributes?.forEach { (key, value) ->
+            newAttrs[key] = value?.toString() ?: ""
+        }
+        newAttrs[AF_CUSTOMER_USER_ID] = cid
+        return CommerceEvent.Builder(event).customAttributes(newAttrs).build()
+    }
+
     private fun parseToNestedMap(jsonString: String): Map<String, Any> {
         val topLevelMap = mutableMapOf<String, Any>()
         try {
@@ -608,6 +688,19 @@ class AppsFlyerKit :
             }
 
         const val MANUAL_START = "manualStart"
+
+        /**
+         * Kit setting: use [USER_IDENTIFICATION_MPID], [USER_IDENTIFICATION_CUSTOMER_ID], or omit for legacy (MPID).
+         * When set to [USER_IDENTIFICATION_MPID] or [USER_IDENTIFICATION_CUSTOMER_ID], AppsFlyer customer user ID
+         * is synced on identity changes and `setUserIdentity(CustomerId)` does not override MPID mode.
+         */
+        const val USER_IDENTIFICATION_TYPE = "userIdentificationType"
+
+        const val USER_IDENTIFICATION_MPID = "MPID"
+        const val USER_IDENTIFICATION_CUSTOMER_ID = "CustomerId"
+
+        const val AF_CUSTOMER_USER_ID = "af_customer_user_id"
+
         private const val CONSENT_MAPPING = "consentMapping"
 
         @Suppress("ktlint:standard:property-naming")
diff --git a/src/test/kotlin/com/appsflyer/AppsFlyerLib.kt b/src/test/kotlin/com/appsflyer/AppsFlyerLib.kt
index c5443c2..2605e3b 100644
--- a/src/test/kotlin/com/appsflyer/AppsFlyerLib.kt
+++ b/src/test/kotlin/com/appsflyer/AppsFlyerLib.kt
@@ -1,6 +1,8 @@
 package com.appsflyer
 
 import android.content.Context
+import com.appsflyer.AppsFlyerProperties
+import java.util.HashMap
 
 class AppsFlyerLib {
     private var consentData: AppsFlyerConsent? = null
@@ -11,6 +13,18 @@ class AppsFlyerLib {
     var customerUserId: String? = null
         private set
 
+    var setCustomerUserIdCallCount = 0
+        private set
+
+    var lastSetCustomerUserId: String? = null
+        private set
+
+    var lastLogEventName: String? = null
+        private set
+
+    var lastLogEventValues: Map<String, Any?>? = null
+        private set
+
     fun setConsentData(consent: AppsFlyerConsent) {
         consentData = consent
     }
@@ -22,9 +36,27 @@ class AppsFlyerLib {
     }
 
     fun setCustomerUserId(id: String?) {
+        setCustomerUserIdCallCount++
+        lastSetCustomerUserId = id
         customerUserId = id
     }
 
+    fun setUserEmails(
+        cryptType: AppsFlyerProperties.EmailsCryptType,
+        vararg emails: String,
+    ) {}
+
+    fun logEvent(
+        context: Context,
+        name: String,
+        values: Map<String, Any?>?,
+    ) {
+        lastLogEventName = name
+        lastLogEventValues = values?.let { HashMap<String, Any?>(it) }
+    }
+
+    fun anonymizeUser(optOut: Boolean) {}
+
     fun init(
         devKey: String,
         conversionListener: Any?,
diff --git a/src/test/kotlin/com/mparticle/kits/AppsflyerKitTests.kt b/src/test/kotlin/com/mparticle/kits/AppsflyerKitTests.kt
index c79c7a6..e2dfbe3 100644
--- a/src/test/kotlin/com/mparticle/kits/AppsflyerKitTests.kt
+++ b/src/test/kotlin/com/mparticle/kits/AppsflyerKitTests.kt
@@ -15,8 +15,6 @@ import com.mparticle.identity.IdentityApi
 import com.mparticle.identity.MParticleUser
 import com.mparticle.internal.CoreCallbacks
 import com.mparticle.internal.CoreCallbacks.KitListener
-import junit.framework.Assert.assertEquals
-import junit.framework.TestCase
 import org.json.JSONArray
 import org.json.JSONException
 import org.json.JSONObject
@@ -85,9 +83,8 @@ class AppsflyerKitTests {
     fun testOnKitCreate() {
         var e: Throwable? = null
         try {
-            val settings = HashMap<String, String>()
-            settings["fake setting"] = "fake"
-            kit.onKitCreate(settings as Map<String?, String?>, mock(Context::class.java))
+            val settings = hashMapOf<String?, String?>("fake setting" to "fake")
+            kit.onKitCreate(settings, mock(Context::class.java))
         } catch (ex: Throwable) {
             e = ex
         }
@@ -123,7 +120,7 @@ class AppsflyerKitTests {
                 .Builder(Product.PURCHASE, product)
                 .transactionAttributes(TransactionAttributes("foo"))
                 .build()
-        assertEquals(mutableListOf("foo-sku"), AppsFlyerKit.generateProductIdList(event))
+        Assert.assertEquals(mutableListOf("foo-sku"), AppsFlyerKit.generateProductIdList(event))
         val product2 = Product.Builder("foo-name-2", "foo-sku-2", 50.0).build()
         val event2 =
             CommerceEvent
@@ -131,7 +128,7 @@ class AppsflyerKitTests {
                 .addProduct(product2)
                 .transactionAttributes(TransactionAttributes("foo"))
                 .build()
-        assertEquals(
+        Assert.assertEquals(
             mutableListOf("foo-sku", "foo-sku-2"),
             AppsFlyerKit.generateProductIdList(event2),
         )
@@ -143,7 +140,7 @@ class AppsflyerKitTests {
                 .addProduct(product3)
                 .transactionAttributes(TransactionAttributes("foo"))
                 .build()
-        assertEquals(
+        Assert.assertEquals(
             mutableListOf("foo-sku", "foo-sku-2", "foo-sku-%2C3"),
             AppsFlyerKit.generateProductIdList(event3),
         )
@@ -183,19 +180,19 @@ class AppsflyerKitTests {
         val expectedConsentValue =
             afConsentResults
                 .getValue("isUserSubjectToGDPR")
-        TestCase.assertEquals(false, expectedConsentValue)
+        Assert.assertEquals(false, expectedConsentValue)
 
         val notExpectedConsentKey =
             afConsentResults.containsKey("hasConsentForDataUsage")
-        TestCase.assertEquals(false, notExpectedConsentKey)
+        Assert.assertEquals(false, notExpectedConsentKey)
 
         val notExpectedConsentKey2 =
             afConsentResults.containsKey("hasConsentForAdsPersonalization")
-        TestCase.assertEquals(false, notExpectedConsentKey2)
+        Assert.assertEquals(false, notExpectedConsentKey2)
 
         val notExpectedConsentKey3 =
             afConsentResults.containsKey("hasConsentForAdStorage")
-        TestCase.assertEquals(false, notExpectedConsentKey3)
+        Assert.assertEquals(false, notExpectedConsentKey3)
     }
 
     @Test
@@ -232,19 +229,19 @@ class AppsflyerKitTests {
         val expectedConsentValue =
             afConsentResults
                 .getValue("isUserSubjectToGDPR")
-        TestCase.assertEquals(true, expectedConsentValue)
+        Assert.assertEquals(true, expectedConsentValue)
 
         val notExpectedConsentKey =
             afConsentResults.containsKey("hasConsentForDataUsage")
-        TestCase.assertEquals(false, notExpectedConsentKey)
+        Assert.assertEquals(false, notExpectedConsentKey)
 
         val notExpectedConsentKey2 =
             afConsentResults.containsKey("hasConsentForAdsPersonalization")
-        TestCase.assertEquals(false, notExpectedConsentKey2)
+        Assert.assertEquals(false, notExpectedConsentKey2)
 
         val notExpectedConsentKey3 =
             afConsentResults.containsKey("hasConsentForAdStorage")
-        TestCase.assertEquals(false, notExpectedConsentKey3)
+        Assert.assertEquals(false, notExpectedConsentKey3)
     }
 
     @Test
@@ -281,22 +278,22 @@ class AppsflyerKitTests {
         val expectedConsentValue =
             afConsentResults
                 .getValue("isUserSubjectToGDPR")
-        TestCase.assertEquals(true, expectedConsentValue)
+        Assert.assertEquals(true, expectedConsentValue)
 
         val expectedConsentValue2 =
             afConsentResults
                 .getValue("hasConsentForDataUsage")
-        TestCase.assertEquals(false, expectedConsentValue2)
+        Assert.assertEquals(false, expectedConsentValue2)
 
         val expectedConsentValue3 =
             afConsentResults
                 .getValue("hasConsentForAdsPersonalization")
-        TestCase.assertEquals(true, expectedConsentValue3)
+        Assert.assertEquals(true, expectedConsentValue3)
 
         val expectedConsentValue4 =
             afConsentResults
                 .getValue("hasConsentForAdStorage")
-        TestCase.assertEquals(true, expectedConsentValue4)
+        Assert.assertEquals(true, expectedConsentValue4)
     }
 
     @Test
@@ -349,22 +346,22 @@ class AppsflyerKitTests {
         val expectedConsentValue =
             afConsentResults
                 .getValue("isUserSubjectToGDPR")
-        TestCase.assertEquals(true, expectedConsentValue)
+        Assert.assertEquals(true, expectedConsentValue)
 
         val expectedConsentValue2 =
             afConsentResults
                 .getValue("hasConsentForDataUsage")
-        TestCase.assertEquals(true, expectedConsentValue2)
+        Assert.assertEquals(true, expectedConsentValue2)
 
         val expectedConsentValue3 =
             afConsentResults
                 .getValue("hasConsentForAdsPersonalization")
-        TestCase.assertEquals(false, expectedConsentValue3)
+        Assert.assertEquals(false, expectedConsentValue3)
 
         val expectedConsentValue4 =
             afConsentResults
                 .getValue("hasConsentForAdStorage")
-        TestCase.assertEquals(false, expectedConsentValue4)
+        Assert.assertEquals(false, expectedConsentValue4)
     }
 
     @Test
@@ -410,22 +407,22 @@ class AppsflyerKitTests {
         val expectedConsentValue =
             afConsentResults
                 .getValue("isUserSubjectToGDPR")
-        TestCase.assertEquals(true, expectedConsentValue)
+        Assert.assertEquals(true, expectedConsentValue)
 
         val expectedConsentValue2 =
             afConsentResults
                 .getValue("hasConsentForDataUsage")
-        TestCase.assertEquals(true, expectedConsentValue2)
+        Assert.assertEquals(true, expectedConsentValue2)
 
         val expectedConsentValue3 =
             afConsentResults
                 .getValue("hasConsentForAdsPersonalization")
-        TestCase.assertEquals(true, expectedConsentValue3)
+        Assert.assertEquals(true, expectedConsentValue3)
 
         val expectedConsentValue4 =
             afConsentResults
                 .getValue("hasConsentForAdStorage")
-        TestCase.assertEquals(true, expectedConsentValue4)
+        Assert.assertEquals(true, expectedConsentValue4)
     }
 
     @Test
@@ -467,21 +464,21 @@ class AppsflyerKitTests {
         val expectedConsentValue =
             afConsentResults
                 .getValue("isUserSubjectToGDPR")
-        TestCase.assertEquals(true, expectedConsentValue)
+        Assert.assertEquals(true, expectedConsentValue)
 
         val expectedConsentValue2 =
             afConsentResults
                 .getValue("hasConsentForDataUsage")
-        TestCase.assertEquals(true, expectedConsentValue2)
+        Assert.assertEquals(true, expectedConsentValue2)
 
         val expectedConsentValue3 =
             afConsentResults
                 .getValue("hasConsentForAdsPersonalization")
-        TestCase.assertEquals(true, expectedConsentValue3)
+        Assert.assertEquals(true, expectedConsentValue3)
 
         val notExpectedConsentKey =
             afConsentResults.containsKey("hasConsentForAdStorage")
-        TestCase.assertEquals(false, notExpectedConsentKey)
+        Assert.assertEquals(false, notExpectedConsentKey)
     }
 
     @Test
@@ -512,7 +509,7 @@ class AppsflyerKitTests {
 
         kit.onConsentStateUpdated(state, state, filteredMParticleUser)
 
-        TestCase.assertEquals(0, appsflyer.getConsentState().size)
+        Assert.assertEquals(0, appsflyer.getConsentState().size)
     }
 
     @Test
@@ -556,22 +553,22 @@ class AppsflyerKitTests {
         val expectedConsentValue =
             afConsentResults
                 .getValue("isUserSubjectToGDPR")
-        TestCase.assertEquals(true, expectedConsentValue)
+        Assert.assertEquals(true, expectedConsentValue)
 
         val expectedConsentValue2 =
             afConsentResults
                 .getValue("hasConsentForDataUsage")
-        TestCase.assertEquals(false, expectedConsentValue2)
+        Assert.assertEquals(false, expectedConsentValue2)
 
         val expectedConsentValue3 =
             afConsentResults
                 .getValue("hasConsentForAdsPersonalization")
-        TestCase.assertEquals(false, expectedConsentValue3)
+        Assert.assertEquals(false, expectedConsentValue3)
 
         val expectedConsentValue4 =
             afConsentResults
                 .getValue("hasConsentForAdStorage")
-        TestCase.assertEquals(true, expectedConsentValue4)
+        Assert.assertEquals(true, expectedConsentValue4)
     }
 
     @Test
@@ -610,12 +607,12 @@ class AppsflyerKitTests {
 
         kit.onConsentStateUpdated(state, state, filteredMParticleUser)
 
-        TestCase.assertEquals(1, appsflyer.getConsentState().size)
+        Assert.assertEquals(1, appsflyer.getConsentState().size)
         val afConsentResults = appsflyer.getConsentState()
         val expectedConsentValue =
             afConsentResults
                 .getValue("isUserSubjectToGDPR")
-        TestCase.assertEquals(false, expectedConsentValue)
+        Assert.assertEquals(false, expectedConsentValue)
     }
 
     @Test
@@ -725,6 +722,129 @@ class AppsflyerKitTests {
         Assert.assertEquals(emptyMap<String, String>(), result)
     }
 
+    // region userIdentificationType
+
+    @Test
+    fun testSetUserIdentity_customerId_legacy_forwardsToAppsFlyer() {
+        setKitSettings(emptyMap())
+        kit.setUserIdentity(MParticle.IdentityType.CustomerId, "ext-cust-1")
+        Assert.assertEquals(1, appsflyer.setCustomerUserIdCallCount)
+        Assert.assertEquals("ext-cust-1", appsflyer.lastSetCustomerUserId)
+    }
+
+    @Test
+    fun testSetUserIdentity_customerId_customerIdMode_forwardsToAppsFlyer() {
+        setKitSettings(
+            mapOf(AppsFlyerKit.USER_IDENTIFICATION_TYPE to AppsFlyerKit.USER_IDENTIFICATION_CUSTOMER_ID),
+        )
+        kit.setUserIdentity(MParticle.IdentityType.CustomerId, "ext-cust-2")
+        Assert.assertEquals(1, appsflyer.setCustomerUserIdCallCount)
+        Assert.assertEquals("ext-cust-2", appsflyer.lastSetCustomerUserId)
+    }
+
+    @Test
+    fun testSetUserIdentity_customerId_mpidMode_doesNotCallSetCustomerUserId() {
+        setKitSettings(
+            mapOf(AppsFlyerKit.USER_IDENTIFICATION_TYPE to AppsFlyerKit.USER_IDENTIFICATION_MPID),
+        )
+        kit.setUserIdentity(MParticle.IdentityType.CustomerId, "ext-ignored")
+        Assert.assertEquals(0, appsflyer.setCustomerUserIdCallCount)
+        Assert.assertNull(appsflyer.lastSetCustomerUserId)
+    }
+
+    @Test
+    fun testSetUserIdentity_email_doesNotUseCustomerUserIdPath() {
+        setKitSettings(
+            mapOf(AppsFlyerKit.USER_IDENTIFICATION_TYPE to AppsFlyerKit.USER_IDENTIFICATION_MPID),
+        )
+        kit.setUserIdentity(MParticle.IdentityType.Email, "a@b.com")
+        Assert.assertEquals(0, appsflyer.setCustomerUserIdCallCount)
+    }
+
+    @Test
+    fun testSetUserIdentity_unsupportedIdentity_doesNotSetCustomerUserId() {
+        setKitSettings(emptyMap())
+        kit.setUserIdentity(MParticle.IdentityType.Other, "x")
+        Assert.assertEquals(0, appsflyer.setCustomerUserIdCallCount)
+    }
+
+    @Test
+    fun testOnIdentifyCompleted_mpidMode_setsCustomerUserIdFromMpid() {
+        setKitSettings(
+            mapOf(AppsFlyerKit.USER_IDENTIFICATION_TYPE to AppsFlyerKit.USER_IDENTIFICATION_MPID),
+        )
+        val mpUser = mock(MParticleUser::class.java)
+        Mockito.`when`(mpUser.getId()).thenReturn(42L)
+        kit.onIdentifyCompleted(mpUser, mock(FilteredIdentityApiRequest::class.java))
+        Assert.assertEquals(1, appsflyer.setCustomerUserIdCallCount)
+        Assert.assertEquals("42", appsflyer.lastSetCustomerUserId)
+    }
+
+    @Test
+    fun testOnIdentifyCompleted_legacy_doesNotSyncCustomerUserId() {
+        setKitSettings(emptyMap())
+        val mpUser = mock(MParticleUser::class.java)
+        kit.onIdentifyCompleted(mpUser, mock(FilteredIdentityApiRequest::class.java))
+        Assert.assertEquals(0, appsflyer.setCustomerUserIdCallCount)
+    }
+
+    @Test
+    fun testOnIdentifyCompleted_customerIdMode_usesExternalCustomerId() {
+        setKitSettings(
+            mapOf(AppsFlyerKit.USER_IDENTIFICATION_TYPE to AppsFlyerKit.USER_IDENTIFICATION_CUSTOMER_ID),
+        )
+        val mpUser = mock(MParticleUser::class.java)
+        Mockito.`when`(mpUser.getUserIdentities()).thenReturn(
+            mapOf(MParticle.IdentityType.CustomerId to "cust-ext"),
+        )
+        kit.onIdentifyCompleted(mpUser, mock(FilteredIdentityApiRequest::class.java))
+        Assert.assertEquals(1, appsflyer.setCustomerUserIdCallCount)
+        Assert.assertEquals("cust-ext", appsflyer.lastSetCustomerUserId)
+    }
+
+    @Test
+    fun customerIdForAppsFlyer_customerIdMode_returnsCustomerIdFromIdentities() {
+        setKitSettings(
+            mapOf(AppsFlyerKit.USER_IDENTIFICATION_TYPE to AppsFlyerKit.USER_IDENTIFICATION_CUSTOMER_ID),
+        )
+        val mpUser = mock(MParticleUser::class.java)
+        Mockito.`when`(mpUser.getUserIdentities()).thenReturn(
+            mapOf(MParticle.IdentityType.CustomerId to "c-out"),
+        )
+        // Same inputs as onIdentifyCompleted (raw MParticleUser). FilteredMParticleUser.getUserIdentities
+        // can NPE in unit tests when dataplan transform returns null; kit UI settings match production.
+        val customerIdMethod =
+            AppsFlyerKit::class.java.declaredMethods.first {
+                it.name == "customerIdForAppsFlyer"
+            }
+        customerIdMethod.isAccessible = true
+        val cid = customerIdMethod.invoke(kit, mpUser) as String?
+        Assert.assertEquals("c-out", cid)
+    }
+
+    @Test
+    fun testCommerceEvent_includesAfCustomerUserId_mpidMode() {
+        val identityApi = mock(IdentityApi::class.java)
+        val mpUser = mock(MParticleUser::class.java)
+        Mockito.`when`(mpUser.getId()).thenReturn(555L)
+        Mockito.`when`(identityApi.getCurrentUser()).thenReturn(mpUser)
+        val mParticle = MParticle.getInstance()!!
+        Mockito.`when`(mParticle.Identity()).thenReturn(identityApi)
+        Mockito.`when`(mParticle.environment).thenReturn(MParticle.Environment.Production)
+        setKitSettings(
+            mapOf(AppsFlyerKit.USER_IDENTIFICATION_TYPE to AppsFlyerKit.USER_IDENTIFICATION_MPID),
+        )
+        val product = Product.Builder("n", "sku1", 1.0).quantity(1.0).build()
+        val event = CommerceEvent.Builder(Product.ADD_TO_CART, product).build()
+        kit.logEvent(event)
+        Assert.assertEquals(
+            "555",
+            appsflyer.lastLogEventValues?.get(AppsFlyerKit.AF_CUSTOMER_USER_ID),
+        )
+    }
+
+    // endregion
+
     // region manualStart tests
 
     @Test