Unable to Join Microsoft 365 Developer Program – Phone Number Already Associated (Error Code 42901)

Question

I’m trying to sign up for the Microsoft 365 Developer Program, but I cannot proceed because my phone number is reported as already associated with an existing developer account. The signup page displays this message:

“Your phone number is already associated with an existing developer account.” Code: 42901

I do not know which account this is linked to, and I cannot continue the registration process.

I have already tried:

• Signing in with all Microsoft accounts I use
• Checking my Microsoft Account security info
• Using different browsers and private/incognito mode
• Waiting and retrying

Based on guidance in Microsoft’s own support responses, Developer Program issues should now be submitted through Microsoft Q&A when troubleshooting steps fail. [learn.microsoft.com]

Could someone from Microsoft please help release my phone number from the old/unknown developer account so I can complete my registration?

Thank you.

Answer 1

Hi Greg Lietzow

The error you’re encountering may occur when a phone number is still linked to a Microsoft 365 Developer Program profile that was created in the past. This association is maintained at the Developer Program profile level, not within Microsoft Account security settings, which is why removing the number from account security info does not resolve the issue.

Please note that Microsoft Q&A is a public, user‑to‑user support forum, and forum moderators do not have access to internal Microsoft systems. We are unable to locate, release, or unlink phone numbers from Developer Program profiles on behalf of users.

• If you still have access to the original Developer Program profile, you can try logging into the Dashboard - Microsoft 365 Dev Center using the account that may have been used previously and delete the old profile. After deletion, the system may take up to 60 days to release your phone number so it can be reused for a new registration. 
• If you no longer have access to the original profile, I recommend contacting Microsoft Developer Support through the following link: Services Hub. Please note that this portal (Services Hub) is a paid ticket and access is subject to certain conditions, which you can review here: Services Hub sign in FAQs | Microsoft Learn.
• If you need to complete registration immediately, using a different phone number is currently the only guaranteed way to proceed.

Kindly let me know how you get on, as your feedback can help others in the community facing the same problem. 

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Answer 2

The Microsoft 365 Developer Program allows only one Developer Program account per phone number. If the phone number is already associated with a different Developer Program account, it must be released from that account before it can be used again.

Use these steps based on the available guidance:

1. Confirm that only one Developer Program account can exist per phone number
   • The program enforces a one-to-one relationship between a phone number and a Developer Program account. If the phone number is already in use, a new Developer Program profile cannot be created with that same number until the original Developer Program account is deleted.
   • To create a new Developer Program account with the same phone number, the existing Developer Program account must be removed first.
2. Try to identify the Microsoft account tied to the phone number
   • If the unknown Developer Program account was created using a Microsoft account (personal) and the email address is forgotten, the Microsoft account sign-in flow can help recover the username using the phone number:
     1. On the Microsoft account Sign in page, choose Sign-in options.
     2. Select Forgot my username.
     3. On Recover your username, enter the phone number that is reported as already associated.
     4. Enter the security code that is sent.
     5. The page will show the email address(es) associated with that phone number; select the one that was used to join the Developer Program and sign in with it.
   • Once signed in with that recovered Microsoft account, go to the Microsoft 365 Developer Program dashboard and delete the Developer Program profile so the phone number is freed. After deletion (and once any program rules such as minimum subscription age are satisfied), the phone number can be used again for a new Developer Program account.
3. Ensure a supported sign-in method is used for the Developer Program
   • The Developer Program does not support signing up directly with a phone number or with an *.onmicrosoft.com address. A supported sign-in identity (work account, Visual Studio ID, or Microsoft account) must be used:
     • Work account (Microsoft Entra ID–backed organizational account)
     • Visual Studio ID (for Visual Studio Professional/Enterprise subscribers)
     • Microsoft account (personal account such as Outlook.com)
   • If a phone number or *.onmicrosoft.com account is used at sign-in, an error is expected and a different, supported email account must be used.
4. If the old Developer Program account is known
   • Sign in to the Developer Program dashboard with the account that owns the phone number.
   • Choose Delete Profile to remove the Developer Program account. This erases profile information and will eventually free the phone number for reuse. Note that subscriptions can only be reissued after the existing subscription has been active for more than 60 days.
5. If the old Developer Program account cannot be recovered
   • When the phone number is already associated with a Microsoft account, the Microsoft account system may present options such as:
     • Using the phone number to sign in directly if it is already an alias.
     • Transferring the phone number from one Microsoft account to another if the Transfer number option is offered.
   • If the transfer option is not available because the number was recently used, the guidance is to wait 30 days and then try again to see if transfer becomes available.

If none of the above steps allow recovery of the Microsoft account that owns the Developer Program profile, direct support intervention is required to release the phone number from the existing Developer Program account. In that case, a support request must be opened so that the support or data protection team can locate the tenant and clear the association.

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References:

• Microsoft 365 Developer Program FAQ
• Welcome to the Microsoft 365 Developer Program
• Help with "phone number is already used" in a Microsoft account