Hi @cgrayson and welcome to our adorable Community π I think I know what might be wrong. When connecting your game with a King or a Facebook account, you have three options like in the picture below.
Β 1. You choose the first option "register with email" if you don't have a King account and you want to create a new one and connect it with your game.
2. You use the second option "register with Facebook" if you want to connect the game with your Facebook account.
3. You use the third option "log in" when you already have a King account and you want to connect it with the game.
I think in this case your husband clicked on "register with email" and he couldn't sign in because his account already exists. He needs to go to "log in" and enter his current email and password which he uses for his King account.
I hope you will find this helpful. Have a wonderful day π€