Use the same Microsoft account password that is set on the parent/organizer account, and make sure it has actually been changed on the Microsoft account site, not just in a local app.
Do the following:
- Confirm the password change on the Microsoft account
- On a phone or PC browser, go to https://account.microsoft.com and sign in with the parent account.
- If the old password still works here, the change in the app did not apply; change it again following the official steps:
- Go to Security.
- Select Change Password.
- Enter the current password, then the new password, and select Save.
- Sign out and sign back in on the same site with the new password to confirm it works.
- Update the password on the Xbox
- On the Xbox, sign out of the parent account.
- Sign back in using the confirmed new password.
- If prompted for security verification (2-step verification), complete it.
- Approve M-rated content using the parent account
- On the Xbox, when asked to enter a password to allow M-rated content, make sure the parent account is the one being used.
- Enter the same new password that was confirmed on https://account.microsoft.com.
- If the password is still rejected
- Change the Microsoft account password again from https://account.microsoft.com using the documented method, then save.
- Wait a short period to allow the change to sync, then repeat the sign-out/sign-in on Xbox and try again.
If the account used on the console is a work/school account instead of a personal Microsoft account, change that password from the My Account portal at https://myaccount.microsoft.com (using Change Password) and then update it on the Xbox.
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