Bill shows unpaid but has been paid already with a credit card,

Hi Bernardett!

I understand that the bills were paid already. Let me show you how we can handle them in QuickBooks Online.

We can create a bill payment to close the bill. Follow these steps:

1. Go to the + New button and select Pay bills.
2. Select a Payment account and enter the details needed.
3. From the list of open bills, select the paid ones.
4. Tap Save and close.

I suggest you check this link on how to manage bills: Enter bills and record bill payments in QuickBooks Online.

If you linked your credit card account to QuickBooks Online, what you'll need to do is simply match the debit transaction to the open bill. This does not just close it but also avoids duplicate entries.

1. From the Banking or Transactions menu, select Banking.
2. Find the downloaded transaction, select it to expand the view, and click Find match.
3. On the Match transactions page, search for the match bill entry and check the corresponding tickbox.
4. Tap Save.

You can check this link for the detailed steps on what to do with the downloaded transactions: Categorize and match online bank transactions in QuickBooks Online.

Also, you may visit this link for more references about vendor transactions: Expenses and vendors.

Keep on posting here if you need more help. Take care!