Cannot connect ITH-20R-O to IBS-M2?

I have several ITH-20R-O sensors but I cannot add any of them to the IBS-M2 gateway.

IBS-M2 gateway itself is reported to be connected but when trying to add ITH-20R-O sub-devices under the IBS-M2 gateway, none of those will appear.

Have tried power on/off the IBS-M2 and removed/inserted batteries from ITH-20R-O sensors but they still doesn’t appear.

When searching sub-devices under IBS-20R-O only IBS-TH-1 to IBS-TH-5 are listed (1,2,3,4 and 5).

As per my understanding ITH-20R-O sensors should be supported by IBS-M2 gateway.

So what’s the problem?

Edit: found the reason, while a bit misleading its those IBS-THx sub-devices you need to add