Hello ,
I can program for you an android vpn app that use IPSec connection method .. I will use java for this app and if you have a design please send it to me and give me the vpn server details and give the plans of the vpn and i will start working ....
-I will use inAppBilling for the plans to get you money sir with secure transition...
-I will use the official Google Vpn Service to create an VPN connection
-I will Use Firebase for the Login/Register system
-I will use FireBase Realtime db to check that the free plan user don't use more than his free quota
-I will use mvp design pattern
-I will make animation in the app design for better ux
If you wanted to use PhpMyAdmin database 'Better than FireBase' I will need more time
Thanks