Most problems are one of these four.
Both devices need to be on the same Wi-Fi network, and both need Local Network permission (Settings › Cribbit › Local Network). Guest networks and networks with client isolation turned on will block the connection. On iPhone 12 and later running iOS 26, Cribbit can also connect with no network at all — both devices need Wi-Fi switched on for that, even without a router.
That is iOS, not Cribbit. No app is allowed to use the camera in the background. Leave the nursery device unlocked and plugged in — the Night screen keeps it dark. Audio does keep running when the parent device is locked.
Cribbit learns the room's own quiet over the first few seconds, so give it a moment after you start. If a white-noise machine is running, raise the sensitivity and the delay together under Alerts. Use Test the alert once in daylight so you know what it sounds like.
Open Cribbit on that device and tap Restore on the unlock screen. The purchase is a one-time, Family Sharing enabled purchase — it covers every device on your Apple Account and everyone in your family group. You never pay twice.
Email kevin@xeve.io and say which two devices you are using and what iOS version they are on.