If rfu 3 bit of MAC header is set to 110

hello. I am currently using chirpstack v4, device lora wan 1.0.3 version. Set 3 bits to 110 in the rfu field in the MAC header. Send unconfirmed date up message from device in ABP mode. However, I get a mic error. I don’t know why the mic error occurs.

Device registration was correct, and normal operation was confirmed when 3 bits were set to 000 in the rfu field.

This is probably because one side does include the RFU bits in the MIC calculation, and the other side does not, resulting in two different MICs.

See also the specification:

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