Invoice mistakenly marked as a paid, How to remove the paid invoice to unpaid?

Hello, @info-ahworldfood.

 I'll make sure you can clear the payment of the invoices accidentally paid. 

We can delete the payment associated with the invoice. It will remove the invoice's paid status.

Here's how:

1. Go to Sales or Get paid & pay in the left navigation menu.
2. Select the Invoices tab.
3. Find the invoice. Click the drop-down button below the Action column and select View/Edit.
4. Click the payment made hyperlink below the PAID payment status and select the date.
5. From the Receive Payment section, click the More button at the bottom and Delete.
6. Click Yes to confirm.

We can also void the invoice and create a new one.

here's how:

1. Navigate to Sales Menu and choose Invoices.
2. Go to the Action column, then select the invoice you need to delete.
3. Hover your cursor over the Dropdown Arrow.
4. Lastly, hit the Void button and recreate a new invoice. 

Once you get the customer's payment, you can record it. You can also create recurring transactions in QuickBooks Online. It allows you to save time and reduce mistakes when making any repetitive entries.

You are always welcome to post there again, @info-ahworldfood. Enjoy the rest of the day.