The server seems to return the wrong EPSG projections.
If I change the projection for this server entry in the JOSM config file (preferences.xml) to EPSG:3857: <tag key='projections' value='EPSG:3857'/>
or if I remove the projections line (<tag key='projections' value='EPSG:6870,EPSG:4326,CRS:84,EPSG:900913'/>) completely, the WMS is working.
Works for me with JOSM without any problems. Entered directly in the dialog at point 6.
The thing is when i remove or change the projections line, it still doesn’t work. Do i just save the file and then it should load normally or should i remove the layer and add it back in? Because it just adds the Projections back in.
Edit: Nevermind, you just need to edit the projections in the xml file and restart JOSM to get it to work. Thanks a lot!