Log into your Account and set your Pubkey in "My Account":
https://i.imgur.com/gloPIeu.png
Once you've set your pubkey, and since free accounts are limited due to very low hash on the pool the following algo is running:
...
I get this error too ... Failed to update your account: Invalid payment ID !
What's the key you're trying to set?
I used pascal wallet on ubuntu . I don't know what was the problem but I tried pascal wallet on windows 10 and now my pubkey has been accepted on suprnova .