MessageExtension apps in Outlook (classic) - GatewayExceptionResponse

[MrKSchmitz]

Teams MessageExtenion apps no longer seem to work in Outlook (Windows Desktop "classic") version greater than 2504 (Build 18720.2000).

The app will fail to load and show a warning/error saying "This feature could not be started. Close this dialog to ignore the problem or click Restart to try again.". Clicking Restart does nothing and clicking Close does nothing. When the warning is dismissed (using the X at the top right) another message is visible stating "GatewayExceptionResponse".

This is not isolated to any one particular add-in. Our add-in (in development and production) does not work, as well as other prod add-ins such as Monday.com or Youtube, as well as Microsoft add-ins like Power Bi.
Later Office versions also have the same issue.

• 2504 (Build 18720.2000) -> Works
• 2509 (Build 19231.20156) -> Broken
• 2510 (Build 19328.20072) -> Broken

[Prasad-MSFT]

Hi @MrKSchmitz, thanks for raising your issue. We will check this at our end and will update you accordingly.

[Prasad-MSFT]

Update:
We have raised a bug for this issue. We will inform you once we get any further update from engineering team. Thanks!