The complete guide to server-side purchase verification & entitlements

This is the long version. If you want the orientation in one sitting, read the short version — a single post covering why client-side checks are advisory, how each store's verification API works, and the pitfalls teams hit. The chapters below take one problem each and go all the way down: what the store actually gives you, what you may store and for how long, how entitlement state changes over a subscription's life, how to keep that state current without a nightly reconciliation job, and which store products grant which entitlement.

Read it end to end if you are building verification yourself, or jump to the chapter matching the decision in front of you. Every chapter is written to be useful whether you build it in-house or hand it to a managed layer.