Gazelle has an API you can use to hook into your 3rd party payment processor if you know how to code. We are working on adding a payment processing feature but we do not support this at this time.
API INTEGRATION WITH YOUR PAYMENT PROCESSORS
Using Gazelle's API you can use hook into your existing payment processing system and link Gazelle's invoices to payments received online. However, you need to know how to code (or hire a programmer) to achieve this step. For access to our API documentation email firstname.lastname@example.org.
GENERIC ONLINE PAYMENT LINKS
If you have an online payment processor you can request a generic payment link and then add this as a default note on all your invoices (and add it to the invoice email template). From here your clients can send you a payment online and put the invoice number in the notes so you can match the payment up with the invoice.