I don’t get any reminders.

Open the iPhone’s Settings, pick the app and make sure notifications are allowed. If a Focus is on, add the app to its allowed apps, or turn on “Last call breaks through Focus” in the app’s settings.

How do I make it stop for today?

Tap Done on any nag, in the app or on the widget. However you wished them a happy birthday (a call, a text, in person), Done ends the nagging for that birthday.

It nags too much (or too little).

In the app’s settings, pick Chill (3 a day), Normal (8) or Relentless (13), and set when the first reminder comes and when the nagging stops. For a single person, choose “Just once” on their page.

Some birthdays are missing.

If you shared only some contacts with the app, add more in Add birthday › Share more contacts, or allow full access in the app’s Contacts setting under Settings › Apps.

How do I move to a new phone?

In the app’s settings, use Export backup and keep the file somewhere private. On the new phone, use Restore from backup. Birthdays saved to Contacts also come along with your contacts.