Hi @Anonymous ,
Your error code indicates that you are trying to use the Azure AD endpoint (likely the one from your B2C tenant). It sounds like they may be getting redirect to the wrong tenant, which you should be able to verify in your browser logs when signing in. See related: https://stackoverflow.com/questions/68868643/getting-error-aadst50013-for-obo-flow-using-azure-ad-b2c-on-net-core-3-1
Otherwise if this is a tenant you could previously access and you believe someone changed the cross-tenant access settings, you may be able to update the cross-tenant access settings by logging in via admin.microsoft.com.
If you believe that your scenario is different, feel free to send me an email at AzCommunity@microsoft.com ("Attn: Marilee Turscak") and include your subscription ID and a link to this thread, and I will help troubleshoot.
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