How can I assign paid Invoice to existing customer?

I have a customer who paid an invoice and the system created a new client ID for him. But, this customer already has a profile with my company. How can I link this invoice to the profile that the customer already has so that he can see all of his invoices in one dashboard?

Not sure I understand, can you explain how the app created a new client record. Are you using buy now buttons?

It sounds like you’d need to clone the invoice, set the correct client and then delete the old one.