How the local connection works in Files To Other Devices
Three separate concepts often get mixed up: a Wi-Fi connection, access to the internet and Wi-Fi P2P. They are not interchangeable.
What this particular app requires
Both Android devices must have Files To Other Devices installed and be connected to the same Wi-Fi network. That network must allow the phones to communicate with each other. Once the app connects the devices, it uses Wi-Fi P2P to copy selected files between them.
Does a Wi-Fi network mean internet is needed?
No. A local Wi-Fi network can connect devices even when it has no working internet connection. For this app, the local network is required; online storage and an internet upload are not required for the described file-copying process.
Why can two phones be on Wi-Fi and still not see each other?
Some guest or public networks deliberately prevent wireless clients from communicating. A firewall or client-isolation setting can also interfere. Merely seeing the same Wi-Fi network name does not establish that all device-to-device traffic is allowed. When discovery fails, check the network configuration before repeatedly reinstalling the app.
What about using Wi-Fi Direct without a router?
Wi-Fi Direct is a technology that can support direct connections, but the supported setup described here is specific to this app. Standalone operation without the required common Wi-Fi network, including phone-created hotspot configurations, has not been verified for this app and is not promised in this guide.