How do I add my own basemap (WMS, TMS, ...)?
If you know of a worldwide basemap that is accessible for free, contact me at tickets@mapspro.uservoice.com so that it can be added to the application.
WMS is currently not supported because most WMS servers don't provide maps with the right projection (global projection EPSG:3857). If you want Maps Pro to support custom WMS servers, please leave a suggestion.