Thanks for your inout, that is probably the way I will have to go. I am also considering creating a consumable called "Monitor / Month" and at the end of each month, sending the user a notification with their usage last month and requiring then to purchase the appropriate number to continue their service - essentially buying consumables in arrears. That is how our present web service works, I just don't know if Apple will approve it?? That does mean that there is the possibility that a user will use for a month and then not pay, but I am willing to wear the cost of that.