Nebula app spins on Android when another VPN app is "always on"

[brad-defined]

We had a couple of reports in Slack about the Nebula app spinning on startup: https://nebulaoss.slack.com/archives/CRWJJM52B/p1654479054750989

Hello, I have the Nebula app on Android 11. When I open it, the main page (where I presume sites are listed) continuously spins (loads). Adding a new site doesn't help. Restarting also doesn't help. I don't see any errors, it just loads forever. I imported the device and CA certificates as generated with the CA binary. Am I missing something?

Frank resolved it by ensuring there wasn't another VPN app marked 'Always On'.

https://nebulaoss.slack.com/archives/CS01XE0KZ/p1655050891622509

Hey, I'm trying to connect my Android phone to my Nebula Network but the app keeps showing the loading symbol. Nothing changes when I'm adding a site

Sebastian reported the same thing, and removing another VPN that's "Always On" resolved it. https://nebulaoss.slack.com/archives/CS01XE0KZ/p1655052142562449

OK the problem was that I had another vpn app enabled as always on

[johnmaguire]

The most recent version of Mobile Nebula changed the behavior here slightly, but we can at minimum improve wording here. Detecting a running VPN would probably be even better. At least currently, only one VPN can be active at a time:

There can be only one VPN connection running at the same time. The existing interface is deactivated when a new one is created.

-- https://developer.android.com/reference/android/net/VpnService.html

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From Jeff Wright on Slack:

In case anyone else runs into this issue: if you have another VPN on an Android phone set to Always-on, Nebula Android will fail to connect with a VPN permissions error. Took me a bit to realize what was going on. Said something like "allow VPN permissions when requested" but permissions had never been requested.

definednetworking.slack.com/archives/CS01XE0KZ/p1681145123777509