Air Wings multiplayer problem

Hi, everyone,

I am playing Air Wings for 1 week, but I can't use multiplayer mode at all. At the very beginning of my gaming, namely, about 1 week ago, I could use the mode and played with my friend. However, for some reason, it won't work now T.T I tried some attempts such as deleting this app and re-download it, turn off the iPad, make sure that restrictions are off, and check Game Center > Me > my account etc.

Details:

1. signed in Game Center in South Korea and moved to Japan

2. iOS is the latest 6.1.2

3. having two apple accounts but none of them works

Please help me T.T