zapier automation

I am looking for a free invoicing software that can send the customer only after they pay, a custom pdf file or message. I am using square invoices, and after the customer pays, I have to send them a bit of custom information like gate and lock codes, I would like to automate that step, that they get their info automatically. Either, 1) by finding a new invoicing system that has the digital download capability, or 2) Possibly setting up a Zapier automation that pulls data from the square transaction and then sends them a file from my google drive. Please assist.