I won a beta code from a wowhead competition which is great! However when I try to Redeem the code it acknowledges that I am claiming a Shadowlands Beta key and my blizzard account so I click on submit and it says oops something went wrong so clearly there isn’t an issue with the code but with me trying to redeem it?
I thought beta keys were not used anymore and that the competition winners get their details forwarded to Blizzard to be added.
Some of the competitions have actual keys despite Blizz initially saying they don’t. A blue confirmed this a while ago.
Congrats Ofthejungle on winning it. I would suggest,firstly, you try logging out then back into your account. If that doesn’t help, try clearing your browser cache & cookies. If that doesn’t help either, all I can suggest is that you send a ticket though it may take a while because of the patch coming tomorrow.
Here is the blue post:
https://us.forums.blizzard.com/en/wow/t/beta-keys-for-shadowlands-updated-august-19/615969
I contacted support. If you have three PTR realms or betas on your account, it won’t let you add Shadowlands beta! Support had to remove one for me so I could add my key 
Apologies, I completely forgot the too many PTR accounts solution. Glad you’ve sorted it out.