The app is an official Apple app: https://developer.apple.com/documentation/wifiaware/building-peer-to-peer-apps.
I have two phones, an iPhone 12 and an iPhone 13, both with Bluetooth turned on and connected to the same WiFi. The devices paired successfully the first time, but after I reset the Wi-Fi identifier in Settings - Privacy & Security - Paired Devices, the devices could no longer pair. Specifically, one device displays a PIN input pop-up, but the other device does not show the PIN. What could be the reason for this?