MTN gameplus online only works on new Sims alone.
So go and get a new MTN SIM and text gm to 2200.
Wait few second or minute to receive a success message then configure preferred VPN like this...
Let's use Psiphon for example,
Proxy sever : game.mtnonline.com
Username : empty
Password : empty
Real proxy type : inject
Real proxy port: 80
Click more option
Vibrate : untick
connection through an
HTTP proxy : tick it
Then tick use the follow settings
Host address : 10.199.212.2
Port: 8080
Untick use proxy authentication
Then goto your PHONE APN SETTINGS
NAME : MTN GAME
APN: WEB.GPRS.MTNNIGERIA.NET
USERNAME : NONE
PASSWORD : NONE