Hello @Ruby Smith ,
Thank you for your question and reaching out. My name is Prakash and I’d be more than happy to help you with your query.
- Please try on the machine itself when you try to join it rather than RDP.
- Make sure you have joined the server to the domain as a domain member and rebooted before trying to promote it to a Domain Controller.
- You have to use an account which is part of the Domain Admin group to join a client to your domain. Also make sure the DNS settings on the client are correct.
- Please verity date and time are in sync .
- Disable IPv6 from both servers
- Check Existing Domain/Forest functional level on 2012 server. minimum level is 2008 support by 2016.
--------
--If the reply is helpful, please Upvote and Accept as answer--