> the app will offer customers access to electronic coupons (redeemable at retail stores) in exchange for an annual subscription fee.
The app is 'selling' two things. One is the discount on the retail stuff and the other is the delivery system to enable those coupons. The delivery system includes that subscription period, displays of coupons available, and however the coupon is presented to the retail customer. The discount component can be sold through a third party payment system - in fact it can't be sold through IAP. But the delivery system is unlocking code within the app and should be sold through IAP. So the question is -what is the real value of the app and the subscription service? Is it all those coupons or is it the cool choose from many coupons and display them conveniently?
Two examples in the extreme -
IAP may be required - the app signals when the user is near a participating coffee shop and displays the shops menu and offers a convenient way of ordering through the app. The user gets $0.10 off a cup of coffee at the shop.
Third party might be ok - the app offers the user a coupon for $1000 on their next car purchase good at any Ford dealer.
Best solution is to divide up the products into two streams. An IAP subscription unlocks app code that provides access to a stream of coupons. Each coupon, or access to a class of coupons, is sold through a third party system at a cost associated with the value of the coupon.