I guess I need to know how a GFCI breaker works with 240V...

I believe with a 120V circuit, if the amount of current on the hot wire
does not equal the current on the neutral wire, the breaker will trip.
The theory being the current is going somewhere unwanted, like through
your heart...

However, with a 240V circuit, with 2 hots and a neutral, how does this
work? It would seem my breaker is tripping if there is any current
difference between the two hots, in which case using 120V is not
allowed.