nRF9160, Using JSON in MQTT command AT#XMQTTPUB

[Stas Jis]

We use nRF9160 on our own board.
The firmware "Serial lte modem" is installed on the chip with connection to an external MCU.

We connect to the broker through the MQTT command, then for the test we publish a message like:

AT#XMQTTPUB="Rigel/ToServer/v2/Operational","Test message with QoS 1",1,0
OK
#XMQTTEVT: 3,0

If we send just a string, everything works correctly. But we need to unload in JSON format, and any attempt to transfer in accordance with the format returns an ERROR to me (I suspect that the matter is in the quote character, but I did not understand how to escape them correctly).

AT#XMQTTPUB="Rigel/ToServer/v2/Operational",{"Test": "message with QoS 1"},1,0
ERROR

AT#XMQTTPUB="Rigel/ToServer/v2/Operational","{"Test": "message with QoS 1"}",1,0
ERROR

[Markus Tacker (he/him)]

See devzone.nordicsemi.com/.../nrf91-serial-lte-modem-mqtt-at-command-for-json-format

[Stas Jis]

Markus,
Is there any other option besides converting JSON to hexadecimal?

[Markus Tacker (he/him)]

Yes, you could use the data mode: developer.nordicsemi.com/.../slm_data_mode.html

[Stas Jis]

Markus,
Maybe I misunderstood, but "data mode" is not combined with AT commands? (including AT#XMQTTPUB).
If all data in the "data mode" mode received from the MCU via the UART bus is considered arbitrary, then how to organize data upload and use MQTT without changing the "Serial lte modem" firmware code.
Maybe there is some example?

[Markus Tacker (he/him)]

Data mode puts the SLM in a state where any data you send to it is forwarded verbatim to the endpoint, until you sent the terminator.

There are example of using the data mode (albeit for other clients) here.