Cannot verify my account through SMS (Error Code: 399287)

Hi, error 399287 means Microsoft has blocked your SMS/phone MFA method via its PhoneReputation system, so the portal won’t send/accept texts for that number, even if it’s yours and the password is correct. It isn’t something you can “fix” on the device; you need to sign in with a different method or have the number unblocked.

Do this, in order: use “Sign in another way” and pick Microsoft Authenticator (the 6-digit code, or passwordless/number-match) or a FIDO2/passkey if you have one; if you can’t get in at all, ask a tenant Global Admin to issue you a Temporary Access Pass (TAP) or to reset your MFA methods so you can re-register Authenticator on your phone; when you’re back in, set Authenticator code as your default and keep SMS only as a backup.

In parallel, open a Microsoft support ticket to request removal of the phone-number block, include the Request ID, Correlation ID, and Timestamp you posted (these let engineering find the event quickly).

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I am having this issue across multiple tenants, including accounts where I am the ONLY global admin and I can't get back into the dashboard.

BTW, calling method is ALSO disabled where SMS method is disabled.

In most cases I have MS authenticator setup and can auth that way.

However, on some older clients, the SMS auth option was the default and now I have no way to access the dashboard to 'require reregistration' or add other auth methods.

Also, it means that clients who want to only use SMS to auth, no longer have that option, they are FORCED to use MS authenticator. I've found that especially my iPhone users hate the app as it's problematic (not receiving popup alerts, copying codes and switching windows not easy on iPhone).

Questions:

1. If SMS is going to be disabled, at the very least we need to be able to use email as the primary auth method. Is there a way to do that?
2. How do we have the number unblocked on PhoneReputation system?
3. In cases where I am locked out as global admin with MS Authenticator not setup, how do I regain access?

Thanks.