Dragon Ball FighterZ Fastest Zeni Farming Method (Money Guide): this will earn you 5300 Zeni per Match (3 minutes) / 1766 per minute / 106,000 per hour.

__________
***UPDATE***:
A NEW & FASTER METHOD HAS BEEN FOUND BY PSN-USER "SlySinatra". IT GIVES 180,000 PER HOUR (+70% INCREASE).

CHECK IT OUT HERE: [ Register or Signin to view external links. ] .
__________

ORIGINAL METHOD (FROM THIS VIDEO - 106,000 PER HOUR):

STEP 0 (PREPARATION):
Beat the Story on normal difficulty. Then you unlock New Game+ HARD MODE. Play through the entire game again on HARD (simply start a new game in Story Arc 1 and choose HARD MODE).
When you reach Arc 3 in HARD MODE you must get 3 x "Victory Zeni Up Lv. 6" skills. They are won from enemies. Arc 3, Map 15 has enemies that drop this skill. You can replay maps to farm three of these skills.

STEP 1:
Replay Arc 3, Chapter 7, Map 13 from the Story Title Screen in HARD MODE. In map select you can press Triangle / Y to switch difficulty.

STEP 2:
Equip 3 x "Victory Zeni Up Lv. 6" in the skill menu. You can stack three of these to increase the effect.

STEP 3:
Farm the match at the top of the map against Goku, Yamcha, Piccolo. The reason being that this match gives a +300 Zeni reward when you win (and the enemies are very weak and quick to defeat).

STEP 4:
Afer the match, pause the game and hit "Retry". Now you get all your health back and can replay the match as often as you want. With loading screens it takes 3 minutes per match if you're just spamming light attacks. If you're actively playing you can do it in 2 minutes.

The key is to get the "Victory Zeni Up Lv. 6" skills. These are only obtainable in Hard Mode in Arc 3. It makes the match reward go from 1800 per match to 5000 (a 277% increase). Furthermore, matches in HARD MODE give 250% more money than matches in normal mode. So this combined with the Zeni skills and the +300 bonus reward for this match makes it the fastest way to earn money in the game.
The trophy / achievement "Set for Life" requires you to earn 20,000,000 Zeni total. To get this much money it will take 3773 matches or roughly 188 hours with this method. Note: you don't have to keep all the money in your inventory, you are allowed to spend it (so if you spent 19 million the trophy pops when you get another 1 million).

Zeni is also used for unlocking two secret characters "Vegeta SSGSS" (unlocks automatically at 300,000 Zeni earned) + "Goku SSGSS" (unlocks automatically at 500,000 Zeni earned).

You don't have to play actively for this farming strategy. Just use light attacks, no directional buttons (press only Square on PS4 / X on XB1). If your characters are level 90-100 it's a guaranteed win. With this method it takes 60-100 seconds to win a match. With loading times and transition screens it goes to 180 seconds on average.