3 wire spa (no neutral/white) is connected to a gfci spa disconnect. Within the disconnect, a white pigtail is connected from the gfci breakerto the neutral bus bar (separate from the ground bar). From the gfci disconnect to the main panel breaker (the 2 pole breaker in the main panel is NOT gfci) there are 4 wires. To connect from the disconnect to the main breaker, does the white wire get connected to one of the (siver) terminals of the breaker (vs the gold terminals where the red and black are connected), or does it get connected to the neutral bus bar in the main breaker?
The white wire gets connected to the neutral bus in the main panel and to the neutral bus in the disconnect. It does not get connected to the breaker. The GFCI pigtail gets connected to the neutral bus in the disconnect and nothing get connected to the neutral terminal on the GFCI. Here's a nice little diagram from SpaCare.com that spells it out nicely.