Symptom

In the 2020 releases or older a map service is set as background map but is not shown.

In PTV Vissim: Network Editor -> Edit basic graphic parameters -> "Show map" = True and Map provider = "MapBox", "OpenStreetMap" or "Bing Maps [Aerial View]".
The map service logo might be displayed but the background in the Network Editor remains white.

In PTV Visum: Edit graphic parameters -> Background map -> "Draw layer background map" = True and Map service = "Bing Maps [aerophoto]", "OpenStreetMap" or any userdefined WMS/WMTS services.
The preview returns only the warning:
"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 used map service might be temporarily unavailable."

Inserting static Internet maps (Insert mode -> Backgrounds -> Network editor -> (left mouse button) -> Internet maps) from Bing Maps or Open Street Map fails with:
- "Tile 1 could not be created, because one or more partial tiles could not be retrieved from the server of the map service."
- "Could not create tile 1. Error code: -1011"

Cause

The framework retrieving background maps was updated with the 2021 versions of PTV Visum/Vissim/Vistro. 
The old framework used by 2020 (and older) versions continued to work until an external change broke the functionality.
Note that any mapservice for OpenStreetMap was already not available anymore for other reasons and is neither covered in newer releases for licensing reasons.

Workaround

Unfortunately there is no workaround for these older releases. We recommend using a newer release. Alternatively, you could use (insert) a background image instead of a map.