How can I find out if a device port is working?

Question

System administration

Good afternoon! There is a device with a 6-pin RJ-12 port. There is a connection cable.
I connect the cable, I try to catch the data, the reactions are 0. In general, 0.
How can I find out if the port is working? There is no other device exactly like it.
Cable RS-232 female to RJ-12. Crimped according to instructions.
All cable contacts rang with a multitester.
Now I have a dilemma: the supplied instructions from the supplier for crimping the cable are incorrect or the device port is disabled (they just didn’t connect the power cable) or the port is simply not working at all.
Is it possible to find out somehow?

I am attaching all the instructions I have.
Foreign manual

Russian manual

Answer 1

Here (on the Vietnamese site) another pinout was googled (yes, it is enough to connect only three contacts - ground, RxD, TxD)
https://thientruongpc.vn/cap-truyen-du-lieu-may-di...

More (matches with Vietnamese version): https://superuser.com/questions/1429837/how-to-con...