I saw that WMS was not supported as basemaps in Web AppBuilder. (Basemaps gallery widget)
I can add one but it does not respond.
I'm using Portal for ArcGIS and Web App Builder for Developer.
It's possible to have WMS as Basemaps in Portal.
Do I miss somethings? or..
Am i the only one who think it would be useful to use WMS service as Basemaps in WAB?