How come, as soon as I turn on VPN, Zoiper loses registration on my Samsung Note 5?

Question

 I am not using STUN, by the way. I find this frustrating, firstly because I cannot receive calls, and secondly, because I have to turn VPN off every time I want to make a call. The VPN service I am using is ExpressVPN. I would be very grateful if someone could offer a workable solution to this annoying problem. 

Comments

Zoiper is now working for me with ExpressVPN. I cannot remember exactly when it started working and neither do I know what was done by whom to make it work. Anyway, it's all good and I'm happy. 

Answer 1

Some VPN services block SIP or the needed ports  by SIP. Additionally there might be some routing/ NAT issue. I can only suggest  that you contact your VPN service and ask them if they are not blocking  SIP.

Comments

ExpressVPN support could not help me but I found a solution. On someone's suggestion, I downloaded another VoIP client called CSipSimple. It works a treat with ExpressVPN. I have always liked Zoiper, bought the paid version and also paid for the G729 codec. Unfortunately, if Zoiper doesn't work via VPN, I cannot continue using it. 

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Last year I went to Oman and I used a trial of Express VPN.  Zoiper did not work, CSipSimple worked perfectly well. 

I went back to Zoiper after I had difficulties with CSipSimple after a stay Belarus and I stopped using VPN for some time.

Last week, I installed Proton VPN and Zoiper continued to work fine.  This morning Zoiper stopped working with Proton VPN.  As I am regularly switching countries, I tried the VPN connection where Zoiper worked a few days ago, but without success.

Any thoughts?

I read some suggestions to ping the IP on VPN first, but how do I do this and how do I use the IP information for Zoiper?

Answer 2

The order can matter. I found that I had to exit Zoiper completely, then start the VPN and pick up the IP, then start Zoiper again -- at which point the registration worked.