I too was having this problem. I was able to resolve it by following this from the FAQ:
"
7. "I cannot connect to the server / I get immediately disconnected"
First, try resetting your modem and router. If that doesn't work, please try opening your Config.wtf file, and removing the server name completely. Restart your WoW client. If the issue persists, open the Config.wtf file and find the line "SET realmName ".....". If this line is present, make sure one of our realm names is inside the quotation. If it is "QA Test Realm ____", change it to the name of one of our realms. (If it is not present, add SET realmName "Desired realm" ). If you are still unable to connect, or need assistance, please pursue help in one of our support channels in Discord or the "Help and Support" subforum."
Best of luck!
