When opening a layer in Map Viewer, the layer is not added and the following error is returned:
Error: Incompatible with current basemap.
When hovering over the symbol, the following warning is displayed.
Error: This layer's spatial reference is incompatible with the spatial reference of the basemap.
This is an expected behavior. Different basemaps use different spatial references. When a layer using a different spatial reference is opened in Map Viewer, the layer fails to be added into the map. In the example above, the tile layer is not compatible with the default World Topographic Map basemap.
There are two potential workaround to add the layer. Use one of the following solutions to solve the issue: