Hi @Aristotelis Papantonis • Thank you for reaching out.
This is a known issue with B2C. When you register for MFA via B2C user flow/custom policy, the strong authentication phone doesn't contain a space between country code and the actual phone number. If you add a space manually after the country code, graph call will return the expected result. The B2C Product group is already aware of this issue and working on it. However, there is no ETA as of now for the resolution.
This is documented here:
- https://learn.microsoft.com/en-us/azure/active-directory-b2c/microsoft-graph-operations#user-phone-number-management-beta
- https://learn.microsoft.com/en-us/graph/api/phoneauthenticationmethod-get?view=graph-rest-beta&tabs=http
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