App-to-Web Checkout

Audience: mobile app developers collecting payments outside the Apple / Google billing systems.
Prerequisites: a backend able to receive webhooks and to authenticate your users.

Principle

Inflow collects the money. You decide who gets access to what.

We deliberately expose no queryable "entitlement" API that your application could call. Your backend remains the source of truth for your users' access rights, fed by our webhooks. This keeps you from depending on our availability in your app's critical path, and saves you from shipping a public key inside your binary.

Your app  ──①──▶  Your backend  ──②──▶  Inflow API (creates the session)
    ▲                   ▲
    │                   │ ④ webhook payment.authorized
    │ ⑤ deep link       │
    │             ┌─────┴─────────┐
    └─────────────┤ Web checkout  │◀──③── the user pays
                  └───────────────┘

The golden rule: the deep link brings the user back, it proves nothing. Access is granted by your backend when it receives the webhook, never on the strength of a URL parameter.

Two flows, two integrations

	App → Web → App	Web → App
Starting point	A paywall inside your app	An ad, a landing page
Is the user identified?	Yes, they are signed in	No, they don't know you yet
Join key	`metadatas.appUserId`	The email entered at checkout
Return	Deep link back to the app	Download + sign-in by email
`returnMode`	`APP_RETURN`	`APP_INSTALL`

This section covers the first one, step by step. The second is covered in Web-to-App Acquisition.

The five steps

Step	What you do	Guide
1	Create the checkout session from your backend	Creating the Checkout Session
2	Open `checkoutUrl` in the system browser	Opening the Checkout
3	Receive the webhook and grant access	Granting Access with Webhooks
4	Bring the user back into the app	Returning to the App
5	Refresh the access right, reconcile if needed	Refreshing Entitlements

Then validate the whole chain in the sandbox — see Testing Your Mobile Integration — and check the Store Compliance rules before you submit your app.

What this builds on

Checkout V2 — the session-oriented checkout these steps use. Read it first if you have never created a session.
Webhooks — the delivery, retry, and signature model your backend must implement.
Metadata — how the metadatas object travels from the session to the payment, the subscription, and the webhook payloads.