My node cannot connect to others

Work through these checks in order.

1. Verify antenna is connected. Most common cause. Never transmit without an antenna attached - it can permanently damage the radio's power amplifier (the PA, the transmit chip).
2. Verify modem preset matches. Two nodes on different presets are invisible to each other. On Meshtastic, check the Meshtastic app - Radio Config - LoRa - Modem Preset; on MeshCore, check the radio/preset settings in the MeshCore app. Ask your local community which preset they use.
3. Verify channel name and PSK match. Wrong credentials mean your messages are encrypted to a key nobody else has. Verify against local network documentation.
4. Verify frequency band. US/Canada = 915 MHz hardware. EU = 868 MHz hardware. These cannot interoperate. Many AliExpress boards ship as 868 MHz by default.
5. Check if other nodes are in range. Meshtastic users: visit meshmap.net to see nearby nodes. MeshCore users: use the MeshCore map at map.meshcore.io. In rural areas you may genuinely be out of range.
6. Verify the radio is transmitting. Check for LoRa init errors in the serial console. A working node shows increasing packet counts in the app.
7. Factory reset and reconfigure. If all else fails, reset and start configuration fresh.