Stripe

Stripe lets your clients pay invoices by card, or by bank debit if you turn it on in Stripe, from the client portal and from the Pay invoice button in invoice emails, one invoice or several at once. The money goes straight to your Stripe account and Quanta records the payment on the invoice. With retainer auto-pay, clients can also save a card so retainer invoices are charged when they are sent.

Connecting, fees, which invoices can be paid and what happens with refunds are covered in Online payments.