Can we include a Pay Invoice button or link on our invoices and accept a payment via Square payment gateway?

Hey Keith,

Thanks for your question - Welcome to the UK community for QuickBooks Online.

Currently QuickBooks only have Paypal and GoCardless as payment providers built into the software directly.

You may be able to achieve this through the "Message on Invoice" or "Memo" or "Description" columns when creating your invoice, or through the use of a Custom Form Style, where the link is added onto one of the content sections, or messages (memo/email/description).

Sometimes, these companies will have a 3rd party app developed to work with Quickbooks, you can search for any 3rd party apps here - https://apps.intuit.com/