Remote Desktop Error Code 0x3 Extended Error Code 0x12 -

This is the true diagnostic. Microsoft’s RDP stack defines 0x12 as a failure in either:

Would you like a script to automate the SPN and trust checks described above? remote desktop error code 0x3 extended error code 0x12

Ensure the returned IP matches the target and that reverse lookup ( nslookup <IP> ) returns the correct FQDN. This is the true diagnostic