Office 365 Office JavaScript APIs not visible in local clients

Question

We have built 2 add-ins, one for Outlook and one for Word, Excel and PowerPoint. They are both add-ins with a command that toggles a task pane. We had no issues accessing them in our own O365 environment using Centralized Deployment. However, when we attempted to deploy them in a partners O365 environment (still using Centralized Deployment) we were unable to get everything to work.

The current state of our add-ins in our partners O365 environment is:

• Can access add-in in Outlook Web and Desktop
• Can access add-in in Word, Excel and PowerPoint Web
• Can not access add-in in Word, Excel and PowerPoint Desktop
  By access I mean being able to add the add-in to the actual application.

We have run both the PowerShell Compatibility Checker and the OAuth checker mentioned in this article:
https://learn.microsoft.com/en-us/microsoft-365/admin/manage/centralized-deployment-of-add-ins?view=o365-worldwide

None of these tools showed any problems with our partners (or our own) O365 environment.

We have also made sure we are running the latest Office versions and that we are targeting specific users or 'everyone'. We have not made use of any nested groups. We also verified that the account we install the add-ins with is global admin.

Other than that we have made a VM with a clean windows and office installation, configured an active O365 account there with actual office licenses (Business Standard) and attempted to add the add-ins there without any success. In this VM we used Fiddler to monitor the 'My Add-Ins' window so we could see if the request to https://<host>/ews/exchange.asmx went through. In the response to that request we could see that GetPrivateCatalogAddIns returned one add-in that is never showed in the Admin Managed tab. Both in these responses from ews/exchange.asmx and from the PowerShell cmdlet Get-OrganizationAddIn the Status/StatusCode property is set to 'Ok'.

We have tried to look for any errors in our manifest file without any success. The Outlook add-in which has a very similar manifest works in both our own and our customers O365 environment.

When we attempted to update our Word, Excel and PowerPoint add-in in our own environment we actually broke the add-in for ourselves, so now our own and our customers environments behave the same way.