Device Not Joining Network via OTAA

Symptom

Customer reports that a newly purchased LHT65N cannot join the LoRaWAN network. The device LED blinks but no data appears on the server console.

Diagnosis

1. Check Device-Side Logs

Connect via USB serial and send:

AT+NJM=?    // Should return 1 (OTAA)
AT+DEUI=?   // Note the DevEUI
AT+APPEUI=? // Note the AppEUI (JoinEUI)
AT+APPKEY=? // Note the AppKey

2. Verify Server-Side Registration

Compare the DevEUI, AppEUI, and AppKey between device output and server registration. Most common cause: key mismatch — especially AppEUI.

3. Check Gateway Coverage

AT+CFM=1    // Enable confirmed mode
AT+NJS=?    // Check join status (0 = not joined)

If gateway is receiving the join request but server rejects it → key mismatch. If gateway is NOT receiving the join request → signal/coverage issue.

4. Common Root Causes

Cause	Frequency	Fix
AppEUI/AppKey mismatch	~60%	Re-enter keys carefully, check MSB/LSB format
Wrong frequency band	~15%	`AT+BAND=?` and match with gateway/server
Gateway not forwarding	~10%	Check gateway connection to server
Device firmware too old	~5%	Update to latest firmware
Duty cycle / channel plan	~10%	Reset channel mask: `AT+CHE=0`

Resolution

In this case, the root cause was AppEUI mismatch. TTN v3 uses a default JoinEUI of 0000000000000000, but the device had a different AppEUI from factory.

Fix:

AT+APPEUI=0000000000000000
ATZ    // Reboot to apply

Device joined successfully within 30 seconds after the fix.

Prevention

Always verify all three keys (DevEUI, AppEUI, AppKey) before deployment
Use copy-paste rather than manual entry to avoid typos
Pay attention to MSB vs LSB byte order (TTN uses MSB)