Automatic discovery needs a direct local connection between the two devices. Having internet access does not necessarily mean they can reach each other.
Check the apps and network first
Open LanSender on both devices. Keep it on screen on phones and tablets, and wake sleeping computers. Check that both devices use the same Wi-Fi or the same router through Ethernet.
Guest networks often isolate devices, even under one network name. Ask the administrator if this happens on a work or school network.
Check system permissions
Allow local network access for LanSender on iPhone, iPad and Mac when prompted. If you previously denied it, enable it in system settings. On Windows, check that the firewall allows the current LanSender app on the network you use. You do not need to turn off the whole firewall.
VPNs, virtual adapters and multiple active networks can affect discovery. Check that the network used by LanSender can reach the other device; ask an administrator to adjust managed settings.
The device appears, but files will not transfer
Check whether the recipient accepted the request, has enough storage, and can write to the chosen folder. Then check that the firewall also allows file-transfer connections.
Look in the receiving folder before retrying. Completed files are kept and do not need to be deleted.
Still not working?
Check that both apps use compatible versions, and update from the website if needed. If the issue remains, send support the operating systems, LanSender versions, connection type and any error message. This is more useful than a screenshot of an empty device list alone.