Map Mavin supports the uploading of layers using  WMS External Tile Service URLs! Please review the following information before proceeding:

Cross-Origin Resource Sharing (CORS) must be configured on your tile service server and you must use HTTPS in order for the tile service to work in most browsers out of the box. If you do not host your own tile service on your own server you likley do not need to worry about CORS.

WMS URLs should set the bbox to {bbox-epsg-3857} and should be in a format similar to this:{bbox-epsg-3857}&SERVICE=WMS&VERSION=1.1.1&FORMAT=image%2Fpng&REQUEST=GetMap&TRANSPARENT=true&layers=mylayer&styles=&srs=EPSG%3A3857&width=512&height=512