Completely by accident, I have a setup that sends a pdf invoice to customers a couple of days after the sale. I’m pretty sure it’s a stripe option I must’ve misclicked.

Anyway- turns out that on the rare occasion someone’s had an issue, this gives them a really easy mechanism to write to me and tell me about it. They let off their steam in the email and then we make things good together. (Yet another reason why I always oppose noreply email addresses)

I still don’t know what or where the setting is, mind.