Glad to have you here on the Community page, @andrea38.
To fix the duplicate payments showing up on your Sales tab, you have to delete the transactions that were added on the bank. Deleting the transactions will affect your bank balance though. However, you can manually check your bank's transactions or reconciliation to ensure the bank register balance will match to your chart of accounts bank balance.
To learn more about fixing balance issues in QuickBooks Online, feel free to read these articles:
Get back to me if there's anything you need assistance with. I'm more than happy to help. Have a good day!
