When the app isn't doing what it should.
If it's still stuck, tell us what the screen says.
Open the iPhone's Settings app, then General → iPhone Storage → Sarx. The version is under the name. It helps us a lot when you report a problem.
Use the form and choose Something's broken. The most useful thing you can tell us is what you tapped, what you expected, and what happened instead — plus your iPhone model and the app's version.
We'd like to hear it. Send it in and choose Feedback — the founder reads every one.
Write to us. A person reads every request and replies to the address you give.