Mobile apps get judged on the interface and abandoned over the backend — the logout that keeps happening, the photo that won't upload, the data that isn't there when the signal drops.
A backend written for a browser on office wifi will fail on a phone in a lift. Mobile changes the assumptions, and the assumptions are the architecture.
Sign-in with Apple and Google, biometrics, token refresh that doesn't log people out weekly, and account recovery that isn't a support ticket.
What happens when the same record is edited on a phone in a tunnel and on a laptop at the same time. Decided deliberately, not by whoever saves last.
APNs and FCM with segmentation, quiet hours, and delivery you can actually audit when someone insists they never got the notification.
Uploads that survive a dropped connection, resized on the server rather than the device, and served from a CDN close to the user.
A local store the app trusts, a queue for pending writes, and a sync strategy — the difference between a real mobile app and a wrapped website.
Versioned APIs and feature flags, because old app versions live on phones for years after you've stopped supporting them.
These are the four issues behind most one-star reviews, and none of them show up in a simulator on a desk.
Building the app itself as well? That's over on mobile development. If the backend also serves partners or a web client, see API development.
Whether the app exists already or is still a design file, tell us what it needs to do offline and at what scale. We'll come back with the backend it requires.