Add WMTS Layer in your map

WMTS is currently not directly support in the Platform.  But you can use a fake XYZ type data source layer in your map and change the source of your base layer. 

1) Then add in your map an XYZ Data source where you want to set your remote WMTS base layer.  Any kind of XYZ Data source of your Library can be used.

2) Create an App with your map and add this javascript code snippet: The layer index (layers[n]) of this javascript snippet code is really important. The index 0 starts at the very bottom layer