I have accidently pressed paid on an invoice, but they have not paid, what do I do?

Hello Showroom2, 

Welcome to the Community page, 

So if you dont need the payment for this invoice yet, if you click into the payment then at the bottom of the receive payment page you will see the option for more if you click that then click delete.  That will delete the payment thank is linked to the invoice and then you will be able to apply the payment when it actually happens.