This is a guide on how to set up Dissidia 012 online play with a PPSSPP emulator on Windows PC. The methods involve sharing an IP address provided by an online connectivity program Radmin, Hamachi or ZeroTier One.

For Android specific instructions, please refer to the appropriate section below.

Crossplay between PC and Android platforms is currently known to be unstable .

Requirements

A PPSSPP emulator build capable of online play (builds since at least 1.1.1 support this)
1 desktop client for online connectivity (Radmin, Hamachi, ZeroTier One)
The Dissidia 012 [duodecim] Final Fantasy game (same regional version for all players)

Be sure to adjust the controls and graphics settings to your liking.

Preparations to ensure compatibility

You must use the same emulator version. If you only intend to play privately, the latest PPSSPP emulator build works too, just make sure all participating players have that version.

NOTE: PPSSPP comes with x32 bit and x64 bit executables. Please ensure that all participants are using either 32-bit or 64-bit when playing. Using 32-bit and 64-bit executables together has been a common cause of desynchronisation.

Game version from the same region. A European version (ULES01505) cannot connect with an American version (ULUS10566) and so on. The Discord community uses the American version (ULUS10566).

If you are unsure about the game version, run it on the emulator and look at the top of the emulator window, it will display the identifed game's name and it's region ID.

Disable firewalls on your computer.

The emulator's "confirm" button set to X in the emulator's settings. Differing confirm buttons will cause a match to end via a desynchronisation in online play when performing EX Bursts with Gilgamesh, Gabranth, Tifa and other characters whose EX Bursts are influenced by this setting.

In PPSSPP's networking settings, ensure that the port offset is set to 5000.

In PPSSPP's networking settings, refresh the mac address by clicking on it a couple times.

If you have other VPN programs like Hamachi or Radmin, they may interfere with each other when used in conjunction with Zero Tier One.

Some people may fail to connect to one another if they have an empty name on their friend card in the game. Please make sure to put a name on your friend card.

Game modifications. Audio, texture and HUD modifications work fine. 3D model swaps do not however, and will result in a network desync.

If players are still failing to connect after the above issues have been addressed, enabling the "enable UPnP" option for both players can also work.

Radmin / Hamachi

Radmin is currently the primary way of connecting online with players in the Discord community. Both Radmin and Hamachi function very similiarly and thus the instructions will be shared for both programs.

Video tutorial (with Hamachi). Same principles, but the program is different.

Install Radmin and follow the instructions by the installer
Start Radmin and press the big red button to "turn on" online connectivity
All participating players must be under the same network in order to connect with each other.
To create a network, move your cursor to the Network field near the top of Radmin, and click "Create network"
Input a name and a password for the network and share the credentials with any relevant players
To join a network, move your cursor to the Network field near the top of Radmin, click "Join network" and input the credentials
Players should now be in the same network. Radmin shows all users within the network, their name and their designated Radmin IP address used for connecting on PPSSPP.

PPSSPP networking settings (shared)

Players should do the following steps regardless of whether they will act as a host for online sessions or not.

Under the "Networking" tab in the PPSSPP settings, do the following:

Enable networking/WLAN
Click on the "Change MAC address" a couple times to avoid a duplicate address from the tournament pack
Port offset should be set to 5000. Never change this.

PPSSPP networking settings (host)

The following steps should be only be done by the player who will act as a host. Only one host is required. This is necessary so that players can connect with the host or other players.

Under the "Networking" tab in the emulator's settings, do the following:

Enable built-in PRO ad hoc server
Insert your Radmin IP into the "Change PRO ad hoc server IP address"
Enter an online lobby or group battle menu to initiate online on your emulator.
Now that online has been activated, let the other player(s) know when you are in a lobby or have a group battle room ready. Communicate your Radmin IP to other player(s) if necessary.

PPSSPP networking settings (join)

The following steps should be done by players who do not act as a host for the session.

Insert the host's Radmin IP into the "Change PRO ad hoc server IP address".
Wait for the host to enter the online lobby selection, an online lobby itself (e.g. Cornelia or Zanarkand) or create a group battle room before attempting to join.
If playing in group battle, every other participant must use the same IP address the host provides.

ZeroTier One

ZeroTier One is an alternative to Radmin or Hamachi, but may yield different results in connectivity and connection stability. If the aforementioned options fail, try this program. Note that it is possible they can conflict with ZeroTier One, however.

Follow the prompts on the screen to install the program successfully.
Run the program, copy and paste 8056c2e21c000001 and click "Join". You should be part of the "earth.zerotier.net" server now.
You can check your Zero Tier IP at the bottom right corner of the program, under the "Managed IPs" row. There may be a "/[number]" (e.g /7) at the end of the IP, this must not be included when adding it to PPSSP's networking settings.
ZTO will run in the background, you do not have to worry about it any further once it's on.
Follow the host / join procedures explained above.

Local play

More recent builds of PPSSPP also support online play locally via multiple emulator instances. This means players can play together with only one computer without using Hamachi, Radmin or ZeroTier One.

Note that the second player may not have sound playback.

Enable built in pro ad hoc server in PPSSPP network settings
Launch your first PPSSPP instance, go to the game and then change the pro ad hoc ip to localhost (just type in "localhost" without spaces or quotes)
Launch your second PPSSPP instance from the same executable or shortcut, it should say "instance: 2" in brackets.
The second PPSSPP instance shares ALL of your saved settings. You may have to adjust controller settings for it to avoid inputting for both players simultaneously and avoid issues when issuing battle requests in online lobbies.

Android

For mobile devices with an Android operating system, the procedure remains largely the same. Most, if not all compatibility preparations apply. The host and join hierarchy also works the same way.

Launch ZeroTier and join the server 8056c2e21c58fb08
Once you have joined the server, your ZeroTier IP can be found right under "Managed IPs". It might have a "/xx" number, that part is not needed for PPSSPP.
After that, follow the network setting instructions outlined above.

Requirements

Download the latest PPSSPP version from the Google Play store
Download the latest ZeroTier version from the Google Play store
A mobile device powerful enough to run the game at full speed.

How to use your own save file

Find your own save file in the emulator's directory (if it is already there), ppsspp/memstick/PSP/SAVEDATA. American version save file is named "ULUS10566GameDataxx" (xx being numbers), European version save is named "ULES01505GameDataxx" etc. Copy that, paste it into the tournament pack's save file directory: ppsspp/memstick/PSP/SAVEDATA.