Your Sera account is currently able to be integrated currently for credit card and/or ACH payments with Stax or with GPI.
Your company might also decide to accept customer payments from some non-integrated partners, such as Zelle, PayPal, Stripe, etc. If you accept payments through these other sources and to maintain proper balance due reports in both Quickbooks and your Sera account, you will want to mark those invoices as paid within Sera.
To do that, you will go to the customer's invoice and accept an External payment. You can put in a note of the actual payment method for your records. This payment will batch up with your integrated payment methods and be sent over to Quickbooks through Saasant, also marking the customer's invoice paid over there as well.
Hint: You might think about marking the Do Not Notify Customer checkbox for this external payment if you have the invoice details communication setting turned on if you have already sent the customer a communication from this other payment method.