I think this kind of came out of nowhere, but Carto is now requiring an API key for all raster basemaps (and soon, vector tiles as well). See: carto.com/basemaps/apikey. So the config needs an option for storing the key, then the tile provider needs to include it, e.g. https://basemaps.cartocdn.com/rastertiles/voyager/{z}/{x}/{y}.png?key={apikey}.
I think this kind of came out of nowhere, but Carto is now requiring an API key for all raster basemaps (and soon, vector tiles as well). See: carto.com/basemaps/apikey. So the config needs an option for storing the key, then the tile provider needs to include it, e.g.
https://basemaps.cartocdn.com/rastertiles/voyager/{z}/{x}/{y}.png?key={apikey}.