If you are getting This device is already enrolled 8018000A error when trying to join a Windows 10 or Windows 11 computer to Azure AD or Microsoft Entra ID.

Open Regedit and look in HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Enrollments – below this key you will find other subkeys with xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx where each x is a hexadecimal number check each looking for a email address from your domain that you are trying to join.  Export out that key, and then delete it, then try to join the domain again.

To join the Entra ID domain, go into Settings, Accounts, Access Work or School Account.  Click Connect button.

Choose Join this device to Microsoft Entra ID