reckon govconnect abn already registered

Hi Sam,
If you're using GovConnect then I can see the ABN was already registered to it back in June 2019.
You're getting that message because its likely you've created a new account under a different email address and then attempting to create an STP entity with the same ABN.

There has already been a submission sent to the ATO for the ABN so I can't delete it from the account its currently under. I'm not going to disclose what the account details are on this public forum but essentially all you need to do is login with the same email address & password that was used when the account was first created.