Issue with Outlook for iOS after changing UPN

While migrating and changing UPN for Azure AD, I ran into issues with Outlook for iOS - "mailbox cannot be added right now please try again later"

Microsoft Support says
Based on the information available in our knowledge base, it seems that the issue you encountered might be related to caching. Outlook and other Office 365 apps cache credentials and configuration details, and when a UPN (User Principal Name) is changed, these cached details can become outdated, leading to issues like the configuration loop you experienced. It is important to note that it might take some time, typically around 48 hours, for the cache to refresh or expire and pick up the new UPN.