Can I change payment status PAID to not paid

Thanks for reaching out to us, belabela.

Yes. If you're referring to a paid invoice, you can find and delete the payment made to change the status from paid to unpaid.

Here's how:

1. Locate and open the paid invoice.
2. Under the Payment Status, click the 1 payment made link.
3. On the Receive Payment page, click More and select Delete.
4. Click Yes to confirm.

The invoice status will return to unpaid after you delete the payment.

I've also included this article that you may use in QuickBooks Online to manage your customers' credits: Handle a customer credit or overpayment in QuickBooks Online.

If there's anything I can help you with, feel free to drop me a reply below. Hope you have a good one.