File transfer troubleshooting: start with the symptom
The second device does not appear
Install and open Files To Other Devices on both Android devices. Check that both are connected to the same Wi-Fi network, and that guest isolation or firewall rules are not preventing local device communication. Follow the permission prompts displayed on your Android version. Close and reopen the app after correcting the network.
The device appears, but connection fails
Keep both devices nearby. Check both screens for a connection request and make sure neither phone has switched networks. If the problem persists, test on a trusted Wi-Fi network that allows phone-to-phone traffic. The app's exact port requirements have not been documented here, so do not change router port-forwarding settings based on guesses.
Copying starts, then stops
Check that the receiving device has enough free storage, both devices remain powered on, and Wi-Fi stays enabled. Retry with one small file to separate a connection issue from a large-batch issue. Before repeating a batch, check which files have already arrived.
The file seems to be missing
First verify that the app reported a completed transfer. Check the receiving phone's Download folder and its configured destination folder. If a file exists but will not open, compare it with the original and try copying it again.
Internet is unavailable
Internet service is not necessary for the local transfer, but both devices still need to share a Wi-Fi network that allows their communication. A phone-created hotspot is not a verified supported configuration for this app.