I have developed an Office add-in. I have trouble with one of my customers. On some Outlook desktop clients, when the function: OfficeRuntime.auth.getAccessToken({allowConsentPrompt: true, allowSignInPrompt: true})
I get the error 13003 (User Type not supported). I confirm that my customer is logged in with his Microsoft 365 account and that he is not on-premises. He is on a recent version of Outlook (16.0.13426.20352).
I am not sure what to do as it works well on the 2 Microsoft organizations I own for tests purposes.
Do you have any idea of what could be not configured correctly?
Modern auth needed to be turned on (kudos to @Outlook Add-in Team).
Mordern auth is Off by default for tenants created before August 1, 2017.