Hi, so there is a way around this. I've played for a week and was frustrated at the start too. The way I found is, you can only use the unlimited diamonds mod for everytime you acquire diamonds.
So for example, you got to level up your town hall rank, you get 50 diamonds. Then quickly go to the gacha and try your luck. But once you do, do not use any diamond related actions.
It sucks, but this is the only way to go around kiarosoft's mod ban. It sucks but hey, i found a way around it.
Few ways of getting diamonds for free:
1. For every monster you defeat for the first time you get a small amount of diamonds.
2. For every town hall rank up grade you get 50 diamonds.
3. Daily challenges reward. Complete one challenge and get diamonds. Use the gacha.
4. Trophy room. For every milestone on each achievement you get rewarded diamonds. This will be your diamond stock pile. Because this game's gacha has a scheduled mechanic that depending on the date, you get s-rank jobs/weapons/items.
The real star of the mod here is the unlimited stamina. I wish I didn't have to go through 5 restarts to figure it out, but yeah, been 2 weeks since i started playing with the mod, but once you get the hang of it's great.