Hayden
It would seem that the air valve is not being activated when depressing the trigger. Possibly the valve has failed, even more likely is paint/cleaner material being allowed to enter the valve while performing maintenance. If foreign material is allowed to enter the valve and dries hard, the valve guts can be stuck closed and you're out of biz.
I don't know if it's possible, but if your trigger is a two part with small elbow near base for flexibility, possibly you don't have the lower part properly positioned on top of the air valve stem. They can be a bit tricky when re-assembling, check to ensure the trigger base is on top of the stem, when correct you'll feel the spring resistance of the valve when depressing the trigger.
If incorrectly placed, the trigger would have a "limp" feeling with no resistance. That's maybe a bit of a stretch, I'm not sure that scenario is even possible, but worth a check.
I'd suggest you have a look at your Iwata manual, see if they give instructions on removing the valve. If not, go to "Don's Airbrush" website and have a look there, he has a couple of Iwata examples and you can likely get some helpful info. Once you get the valve out, you can check to see the cleanliness state.
If it's just a bit mucked up, you might be able to clean it up and use a TINY bit of lube to free the action. I've used a very minute film of coconut oil on the o rings of air valves before, to restore freedom of movement when they got sticky with age.
Best of luck with it, please let us know how it goes for you.
Patrick