How to Create and Join Custom Matches

To create a custom match, follow these steps:

Go to the Menu - Settings - Developer;
Select Custom Matchmaking;
Enter the Matchmaking ID. Matchmaking ID will let other players join your game. Use whatever ID you like, but make sure to remember it;
Tap Confirm.

You will be queued for a custom match right away. Now all you have to do is send your Matchmaking ID to the leader of the enemy team and wait for them to join. The match will start immediately once everyone has connected.

NOTE: Custom matches allow you to select which map you want to play on. The Matchmaking ID should start with the map ID. Below is the full list of maps available in the game and their corresponding IDs:
dm depot — Old Depot (Capture the Bag)
dm tlensk — Tlensk City (Capture the Bag)
dm area — Area 39 (Capture the Bag)
dm ship — Cargo Ship (Capture the Bag)
dm station — McReady Station (Capture the Bag)
dm sky — Skyscraper (Capture the Bag)
dm village— Village (Capture the Bag)
dm plane — Aircraft Graveyard (Capture the Bag)
ct depot — Old Depot (Control)
ct tlensk — Tlensk City (Control)
ct area — Area 39 (Control)
ct station— McReady Station (Control)
ct ship — Cargo Ship (Control)
ctd area — Area 39 (Team Deathmatch)
ctd ground — Shooting Ground (Team Deathmatch)

Joining a custom match is exactly the same. If you already know the Matchmaking ID of the host, just put it into the Menu - Settings - Developer - Custom Matchmaking. It takes a few seconds to find the game, then you are ready to start playing.