AT+CMUX MC7354 / MC7304

Does AT+CMUX work on these cards? We’re trying to CMUX / multiplex these cards. Please, any advice would be great, every time we run AT+CMUX we get an error.
For example, if we send the AT-commands:

Both return error. Are we setting something up improperly or is this just not implemented at all? We find it strange that a device with a single UART does not have the ability to be multiplexed?

Are we missing a step, is it a firmware issue? Any help would be greatly appreciated.

I did some digging and eventually found the AT-command book for the MC7xxx models and it says its supported but makes the note of: “When MUX mode configured on USB Interface” What does this mean?

I have attached a snippet of the pdf showing the AT-command and the proof that it is ‘supported’ by the checkmark but we don’t know what to make about the note.
Are they talking about the COM port / USB port of the card? For example in linux to send AT-commands to these cards its /dev/tttyUSB2 ?

Remember the AT Command reference is for a wide range of modules with different chipset variants.

If your talking in regards to the MC7354 and MC7304 specifically (which has the MDM9615 chipset i believe), the QMI feature of the hardware / firmware already does the same thing that the CMUX command does, in the sense of presenting different interface channels for different services (AT, DM, NMEA). Except, instead of multiplexing them over a single endpoint of the module, separate dedicated endpoints are used for each service.

I think the “When MUX mode configured on USB interface” note you’re quoting is in reference to older modules that still use the old DIP interface framework (Certain MDM9200 chipsets and older).