How to enable always-on VPN on Android 6.0.1?

Question

Android

Available: ASUS ZenFone 2 Laser (Z00ED), Android 6.0.1, PPTP server.
I create a VPN connection, enter an account, click the "save credentials" checkbox, connect - everything works.
Next, I want the VPN to work constantly, I click in the upper right corner of the property, in the drop-down menu I click "Permanent VPN" and there in the window there is only the "Do not use" item. My network is not in it, so I can’t select it.
Tell me what am I doing wrong?

Answer 1

I observe the same on some phones, usually adding a few more vpn connections (not necessarily existing \ real \ working ones) helps - a list appears there