Ive just clicked on received payment button on a client but it was the wrong client. how can i reinstate the first invoice and mark it as unpaid?

I can guide you through reinstating your paid invoice, @simon58.

You'll have to open the invoice and remove the payment associated with it. This way, the invoice status will change to unpaid.

Here's how:

1. Go to Sales and then choose All Sales.
2. Look for the paid invoice and then open it.
3. Select the payment link and then tap the Date.
4. Remove the checkmark next to the invoice number to unlink.
5. Click Save and close and then Save as credit when prompted.

Once done, go back to the Receive payment window and then apply the credit or payment to the correct invoice.

Feel free to browse this link to help you in managing customers: Topics about your company's income and customers.

Please know that you're always welcome to swing by if you still have questions or concerns with invoices. I'm always here for you. Take care and have a wonderful day ahead.