MFA & Verification Issues

How to Fix Microsoft Signup Error 40315 (Phone Number Check)

Bushra Parveen Oct 8, 2026 868 views

Question details

The user is unable to complete the Microsoft account signup process due to a phone number validation failure.

Product: Microsoft Account
Device & OS: not provided
Scenario: Attempting to register a new Microsoft account or accessing the Microsoft 365 dashboard using a mobile phone number.
Observed behavior: The system rejects the signup attempt and displays error code 40315, indicating the phone number did not pass security checks or is already associated with another account.

Before you start

Before troubleshooting, ensure you are using a standard mobile carrier number (not a VoIP or virtual number), and keep the exact error code and correlation ID from the error screen handy.

Solution 1Recommended

Verify Phone Number and Unlink Existing Accounts

Use this method to ensure your phone number complies with Microsoft's security policies and isn't locked to an inaccessible account.

Microsoft restricts phone numbers from being registered to multiple accounts simultaneously to prevent spam. If your number is already tied to an old account, it will trigger error 40315 during new registrations.

Check existing accounts

Try signing in to Microsoft using the phone number instead of an email address to see if it routes you to a pre-existing account.

Use an alternative number

If the current number is blocked or locked, restart the registration process and input a different, valid physical mobile phone number.

Use an email address

Click on 'Get a new email address' or 'Use your email instead' during the signup prompt to bypass the initial phone number requirement.

Verify Phone Number and Unlink Existing Accounts

Virtual Numbers Blocked: Microsoft security checks automatically block VoIP, Google Voice, and other virtual numbers. Always use a standard cellular carrier number for verification.

Solution 2

Contact Microsoft Support with the Correlation ID

If your valid phone number continues to fail security checks, you will need Microsoft Support to manually unblock it.

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Frequently Asked Questions

Can a phone number be registered for only one Microsoft account?

Yes, Microsoft typically restricts a phone number to a single account to enhance security and prevent spam. If you try to reuse it for a new account, you may encounter error 40315.

What does 'failed security checks' mean when creating an account?

This error means Microsoft's automated system has flagged the phone number. It usually happens if the number is virtual (VoIP), associated with suspicious activity, or used for too many recent verification attempts.

Where can I find the correlation ID for error 40315?

The correlation ID is a unique string of letters and numbers displayed directly on the error screen when the signup fails. It is essential to provide this code when contacting Microsoft Support so they can trace the issue.

Login & Account Issues