Can I set AAD app registration to be multi-tenant if it is pointing to azure function in the another tenant?

Question

I have an Azure Function deployed on tenant A. This function is accessed from the tenant B where it's secured with AAD App Registration.

I need to activate Multi-tenanted property. App ID URI points to the azure function in the tenant A

When I change the Multi-tenanted property to yes I'm getting this error:

Failed to update App ID URI application property. Error detail: The App ID URI is not available. The App ID URI must be from a verified domain within your organization's directory.

I understand that App ID URI has to be in the trusted domain, but I have no idea how can I do it. Is it even possible? The Azure Function has to be in the tenant A. Can I add somehow new record here /ActiveDirectoryMenuBlade/Domains and make it work?

Answer 1

To change your app's app ID URI, use the Azure portal to navigate to Azure Active Directory > App registrations > (choose your app) > Expose an API.

If you haven't set an app ID URI yet, you will have a "Set" option at the top. If you've already set a value, you will have an "Edit" option to change it.