Email us at support@sharedtimer.app and we'll get back to you.
The alarm didn't make a sound. Check that notifications are allowed (Settings → Notifications → Shared Timer), and note that the silent switch and Do Not Disturb mute alerts.
A shared timer isn't appearing. Make sure you're signed into iCloud (Settings → your name) and opened the share link on the phone with the app installed.
I paid but sharing is still locked. Open the unlock screen and tap "Restore Purchase" while signed into the same Apple Account you purchased with.
Can someone else edit my timer? No — only the person who created a timer can edit or cancel it.