In my use case, I provide a one-time service to a client and therefore have no real use for a portal as a client will almost never receive multiple invoices from me.  I don't want to send extra emails and confuse the client by requesting that they sign up for the portal.

All I need is for the client to be able to click on the invoice and pay it (or part of it).  I have the gateways set up through Square.  It works well.

How do I disable the portal?  Or at the very least, keep the clients from getting emails that suggest they join my portal?

Thanks!