Add ArcGIS REST Tile service in your map

1) The first step, be sure the ArcGIS Rest web services support WMTS protocol.  Open the web service in your browser and be sure you see WMTS in the support services list

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

3) 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