A190 Pair with M300

Hi, M25 Phone pairs all ok to the M300 no issues. 

My issue is when i try to pair the A190 headset, it shows as connected to the SIP but disables the phone from ringing so  ive no idea if anyone is calling. 

If im told my phone is ringing i can press the call answer button on my headset and take the call 

i have per setup instructions disabled call groups and followed these instructions.  How do I pair the A190 headset with an Mxxx series DECT handset

however im not able to pair it as per step 3. In the pull-down list of "Paired Terminal", select the "Terminal Idx" of the handset.

the drop down wont show anything.

Everything is updated to latest firmware.

Any help would be greatly appreciated.

Thank you.