If using his IP as PRO adhoc server and you can't connect to his IP it meant his ports are blocked (which is also why he can't see your hosted room when using your IP), or he forgot to enable built-in Adhoc Server.
If you are using VPN (ie. hamachi) don't use public Adhoc Server (ie. socom.cc, etc.), otherwise the connection won't go through VPN, which meant it will need port-forwarding.
If you are using VPN (ie. hamachi) don't use public Adhoc Server (ie. socom.cc, etc.), otherwise the connection won't go through VPN, which meant it will need port-forwarding.
PPSSPP Multiplayer Guide: https://github.com/hrydgard/ppsspp/wiki/How-to-play-multiplayer-games-with-PPSSPP