"That is correct. By pulling 120 volts from one side of a 2 pole GFCI
breaker you are creating an imbalance which trips the breaker by
design. If
your hot tub requires a 240 volt circuit and a 120 volt circuit you
will
need to run a separate 120 volt line. You cannot tap off of one side
of the
two pole GFCI breaker. Did your electrician know about the 120 volt
requirement when he installed the wiring? "

That's strange, cause I have a 240V line with GFCI in the breaker box
that is run to my spa. It's a conventional 240V line, two hots,
neutral, ground. The spa uses 240V only for the heater, everything
else is 120V. And it works! I assumed a 240V GFCI worked by making
sure that the sum of the currents on the two hots and neutral was zero.