One-way audio issue after replacing two Grandstream phones

Hello,

I have two VLANs connected via FortiGate 40F:

VLAN 40: phones, PBX, and PCs

VLAN 10: servers

The network is working fine in general. However, after replacing two old phones with new Grand stream models GRP2602P, I started facing the following issue:

Scenario 1: When I call an old phone from a new phone, only I can hear the audio, but the other side cannot hear me.

Scenario 2: When the old phone calls the new phone, both sides can hear each other without any problem.

Scenario 3: When I call between the two new phones, everything works fine (two-way audio).

Scenario 3: when I Make call for outside calls everything fine
So the issue only happens when calling from a new phone to an old phone.

Could you please advise what might be causing this problem and how to solve it?

some people say this problem from FortiGate

Thank you.