Not working for some reason

I was using this app for a long time on my iphone. I bought an iPhone 7Plus recently and it was working fine. All of a sudden when i am on cellular connection the app does not open. Keeps giving me an error message. But it is fine if Im connected to wifi. Never had this problem before. I have unlimited data now I cant use my data to use the app. Hopefully the app developer fix the problem asap!!!!

Update: just updated the app. Cause there was a new version which supposed to fix the data connection but it is still not working. The app is loading this time but cant make any call over cellular data. It says no connection which is crazy. Fix it please.....

Juthee about BOSS Revolution: Calling App, v2.5.4