I have same issue for a sim that I have put into apple phones. Earlier it was in iphone 6s and now in new iphone SE. The virgin mobile app has never worked. The message I get is "We are having difficulty reaching our servers". I had this odd sms conversation with support and they kept asking silly questions. e.g. have you restarted the phone, have you reinstalled the app, can you connect to internet, social media... (I mean I have changed the phone).
But the adviser really was not good. His/her view was - its my iphone's problem.
Which phone do you have ? Apple or android ?
I have a second sim (separate virgin contract). I have always used that in android phones, over last 5 years. And the app has always worked on it.