Why doesn't DTMF work over VPN but does locally?

Question

I installed Zoiper on my Note 8 and Tablet. When connected to my wifi Zoiper has no problem navigating the IVR on my Freepbx system. If I connect via VPN  from outside my network neither device manages to pass DTMF tones. I can call into the voicemail and make/receive calls locally or remotely.only DTMF do not work over VPN. 

There aren't any weird firewall rules setup on my firewall for the VPN. I'm using a Ubiquiti USG Pro 4.

MizuDroid works fine over the same VPN and devices passing DTMF. The bluetooth doesn't work on it so I tried Zoiper. Zoiper bluetooth works flawlessly. Now if I can get DTMF to work.

Comments

Hi,

Try to use different codec and see if it will make any difference.