Outgoing call issue


Im using Grandstream PBX and WP810Handsets with a SIP trunk.
I have already setup the sip trunk and outgoing calls and incomming calls works fine.

However i have 2 issues that i need support from your side.

  1. When i make a outgoing call to a specific number (till now i have noticed only 1 number), I can hear the sound but the person on the other side cannot hear me. When i use my personal mobile or another PBX to call, it works fine. This happen only for 1 phone number.

  2. When I use my WP810 handsets to make outgoing call for another office that has DISA setup, i cannot enter the code to pass the call. For example when i dial 123 (outgoing call - another office), i can connect here the voice. Automatic message from the PBX in that office asks to press a number for a specific task and when i press the number nothing happens. But however when i press the the number and then hold key in my phone, the call passes to the proper location.
    For this i have also tested with a soft phone installed to my pc (ZOIPER). when i use zoiper everything works perfect and i dont have to press hold to pass.

Would appreciate it if someone helped me in this issues.