Payment button and existing client accounts

Is there a way for me to create a payment link/button and have it linked to customer existing account? My customers purchase items from me on continues basis but not at exact same time intervals, so I can’t really use the recurring payment option. The problem that I have now is that when a customer purchases an item from me the system automatically creates a new customer profile. So I end up with 10 different profiles for the same customer.

I want to find a way to make sure that when a client purchases an item from me using the buy link/button it is automatically linked to their existing account without creating a new one.

It’s possible to link the invoice to an existing contact by adding the &contact_key=<value> to the link. If you’re self hosting you can see contact_key in the contacts table in the database, if you’re using you can access it with our API.