"Payment gateways have not been set up yet."

"Payment gateways have not been set up yet."

I keep getting this error when I try to email an invoice, despite the fact I've (seemingly) synced my Paypal and Stripe accounts. What do I need to do to get this working? Error is below.

Online Payment Options

Payment gateways have not been set up yet. Please set up a payment gateway for online payments or remove the online payment link in the body of this email.