tasminsimmonds lol you didn't even answer the question
@jaygummers this is just a basic search as I too am curious about this and would like to see you solve this but here are some helpful links that may help you get where you're going. P.S. please update once you have an answer to this question, again, I would love to know what you find out.
(start with this one, apparently IAP is the way to go for in-game purchases for Construct)
(this seems to be a tutorial on implementing in-game purchases)
(this doesn't seem related to Construct but may help you)
(this is also talking about IAP)