I have the client's credit card data. How do I make a payment?

If the invoices are already created in CONTACTS > CLIENT NAME > INVOICES “View All”, you can login as the client in CONTACTS > CLIENT NAME > Login as {Client Name} (top right corner), then go to the PAYMENT tab, select the invoice(s) and click on the button "Charge my Card". An Authorize.net payment form will load, where you need to fill out the needed credit card data and finish the process.