If you are using a VPN app it may be intercepting and proxying web traffic for you (whether you realize it or not). This would explain why it works when you ‘turn off the vpn’.
If your VPN provider requires an app, well, that sucks and you should consider using another provider that does not.
Given that these same objecting companies have had tens of thousands of Indian developers, with source code access for iOS and Android, on their payrolls for decades now … I am not sure why they would suddenly be worried about this now.