6 weeks ago I connected my Epygi PBX WAN port directly to my ISP device, to start using the zoiper service.
I configured my SIP extension on the PBX to Other.
I entered the Public IP of the ISP device into the host address field of my Zoiper android application and added :5060 at the end. e.g. xxx.xxx.xxx.xxx:5060
This worked well for the first few weeks. However, in the last 3 weeks every night registration fails (408).
In the morning, I would reset my ISP device, a new Public IP would be assigned and then I would enter the new Public IP into the host field of my Zoiper application and it will work instantly for another 12hrs. The next morning I would repeat this process again and again for a temporary fix.
My boss is using premium zoiper services and we all experience the same problem at the same time.
What is required to keep my service running continuously?