Symptom

When choosing OpenStreetMap as map service the following error messages (or similar) may occur:
Unable to call background map with the current settings.
Background map could not be called by server of the map service used.
Check the parameters of the used map service and your internet connection.
The server of the map service used might not be available temporarily.

Cause

We have identified that the map service OpenStreetMap cannot be loaded anymore from PTV Visum/Vissim 2020 (and older) since July 2022. 
This is caused by changes implemented by the openstreetmap.org community.
Note that since the introduction of PTV Visum/Vissim 2021 the Background map 'OpenStreetMap' is not offered anymore, as the map service 'OpenStreetMap' is not intended for commercial purposes and its use lacks any contractual basis:
https://operations.osmfoundation.org/policies/tiles/

Workarounds

For PTV Visum 2020 and older:

- The map service "WMS TopPlusOpen" https://gdz.bkg.bund.de/index.php/default/wms-topplusopen-wms-topplus-open.html for which an URL template as XML file is attached.

- The map services offered by Munidialis https://www.mundialis.de/de/ows-mundialis/ when complying with the OpenStreetMap license URL templates as XML file is attached.
It contains 3 URL templates which can be used as a replacement for OpenStreetMap.

To add them as map services the contents of the XML file are added to the User preferences:
Edit -> User preferences -> Open
The PTV Group is not responsible for these map services which might be slower.

Note: For PTV Visum 16 and older: Replace "https" by "http".

For PTV Vissim/Vistro 2020 is no workaround available and we recommend to use the Map services offered with PTV Vissim/Vistro 2021.

Resolution

Since PTV Visum/PTV Vissim 2021:

Neither any user defined map service added to
Edit -> User preferences -> GUI -> Background map
contacting OpenStreetMap (or Google) will not work without any license.
Instead, the map services MapTiler and 'PTV ...', rendered by HERE and partly based upon OpenStreetMap data are offered.

These are available in:
Graphics -> Edit graphic parameters -> Background map -> Map service