Check these in order.
You buy it once on the App Store and that's it. No subscription, nothing to buy inside the app, no ads.
Not if you use Apple Family Sharing. When the family organiser turns on Purchase Sharing in iOS Settings → your name → Family Sharing, family members can download BabyRhythm for free from Purchased in the App Store.
Without Family Sharing, each person buys their own copy.
Sign in with the Apple Account you bought it with and download it again from Purchased in the App Store. Your records live in iCloud, so they come back when you reinstall.
Tap Start timing now in the feed sheet. You can also start and stop from the Lock Screen widget button. If you forget to stop it, it closes itself at 60 minutes, so a forgotten timer at 3 a.m. doesn't leave a strange entry.
Touch and hold the Lock Screen, then Customize → Lock Screen and add BabyRhythm above or below the clock. The widget shows the next expected feed time.
Settings → Notifications has two switches. Notify at next feed time is off by default — that default exists so the app doesn't ring in the middle of the night. Notify me when it differs from usual tells you once in the evening when your baby's rhythm has clearly shifted for two days in a row. It's an observation, not a health judgement.
From inside the app: Settings → Share with family → How sharing works → Report a problem. Sending it that way fills in diagnostic details, which makes the cause much easier to find (you can read all of it and delete anything before sending).
Or email directly: babyrhythm.help@gmail.com
This is made by one person, so a reply may take a day or two. Thanks for your patience.