Latest version of Zulu for Android Won't Connect to FreePBX

Hello all,
Not sure whether I’m doing something wrong, or whether there’s some sort of possible configuration glitch, but for some reason, whenever I connect to Zulu on my Android phone, nothing happens; the account is recognized, and seemingly Zulu will connect to FreePBX, but then nothing; “account is closed” error message from Zulu. Latest Android and latest Zulu. I also have a VPN connection on my phone since T-Mobile seems to have a thing for blocking the SIP protocol, but if any more information is needed, let me know. Help on this wouldbe appreciated. Others in my group do not have this problem, but they have iPhones. I’m so far the only one with the issue.