Bought coffee with Curve card ~20 days ago from vending machine which was in rather remote location - no idea how they process payments.
Request for payment never came.
Did I get free coffee? 
In how long time frame merchant can claim payment as delayed/offline transaction after purchase?
I would say probably not. It will be debited, when is anyone’s guess…
P. S. If it turns out it’s not debited, tell me and I’ll have a cup of coffee there as well. 
@patrice58: You were right. No free coffee this time 
- purchase got reserved from linked card more than 30 days later
Thanks for the update.