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- Incorrect credentials and keys
- Downlink issue
- The gateway hit the duty cycle and is not able to send a join accept
- There is a slow connection from the server to the gateway, as a result the join accept message is sent too late (this can happen when a gateway uses 3G as a backhaul)
- Overused App nonce. App nonces are unique identifiers used during the join request, if the device performs too many join requests, it will eventually run out of nonces. If your device joins the network with a high frequency, you need to review your device join policy. For example, should the device be in deep sleep during between each message it doesn't have to rejoin once it wakes up as it can store the network keys ("mac save" for RN2438 module).
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