iOS 12 VPN authenticatino message keeps poping up

I just upgraded to iOS 12 and I have a VPN app North VPN. I keep getting a pop-up asking me to "Enter your Authentication information" and will not let me do anything else. I had to keep canceling and try to type something before the pop up came up again. Eventually I was able to delete the VPN app.

Is this a North VPN issue or and iOS issue? How to I fix it?

Thank you