Transfer issue Polycom VVX150/250/350/450 with Windows App

[astrae]

Hi,

We look after a site with Polycom phones. They came from 8x8 originally.

They have been using this setup fine for 2 years on 3cx.

They use the windows App with "Deskphone control" in the App on the poly phones.

Recently users are having issues transferring calls. They receive an error in the app "MakeCall source is not reachable" They can still make calls and answer calls.

It may not be across all models but I have definitely seen it across 350's and 450's.

Phones are on the latest Firmware (6.4.3.5018)

Windows clients are 5.5 (1096)

A reprovision of the handset fixes the issue straight away. Users can transfer calls after that.

I have setup handsets to reboot overnight but this hasn't been enough to fix the issue, I'm not sure how often the handsets self "reprovision"

Is anyone else having issues?

 

[myitbrainHQ]

Polycom VVX phones are end-of-life and unsupported by 3CX, but you have options here.

The transfer issue with the Windows app is almost certainly a SIP re-INVITE handling mismatch. VVX legacy firmware sends a REFER for attended transfers, while the 3CX Windows client expects the PBX to mediate via UPDATE/re-INVITE. When signaling mismatches, you get silent calls or dropped transfers.

Things to try:

1. In 3CX Admin, find the VVX extension and toggle the "Disable re-INVITE" setting.
2. On the VVX under Settings > SIP > Advanced, set SIP Transfer Type to REFER (not Replace header).
3. Upgrade VVX firmware to latest 5.9.x - there were transfer SIP bug fixes in later builds.
4. Practical workaround: have users initiate attended transfers from the 3CX Windows app rather than the desk phone - this sidesteps the VVX SIP behavior entirely.

If audio still drops mid-transfer, check your NAT/STUN config - RTP anchoring issues can masquerade as transfer failures.

 

[astrae]

Thanks for your Reply.

Firstly these VVX phones are supported by 3cx and are auto provisioned and have firmware pushed by 3cx so I would be very hesitant moving from v6.4 to v5.9.

1. There doesn't appear to be any "Disable re-INVITE" setting in 3cx.
2. I couldn't find this setting in the phone
3. as above.
4. All transfers are done via the app. I never mentioned transfers from the handset itself.

Audio dropping mid transfer? I don't have this problem and never mentioned it?

Thanks for the suggestions but this almost seems like a copy paste suggestion from bad AI?