You will have to check the code on this, but it is highly likely you
need a separate disconnect box. I put a hot tub in a couple of years
ago in a house I owned. There were pretty specific instructions on the
electrical work. I had a three pole disconnect with ground. Ran line
to the hot tub. From the disconnect box, I ran the same three
conductor + ground to my main box, which had a two pole GFI. Don't
remember the wire size, but it was pretty heavy stuff. The usual
clamps, etc.

When away, or servicing the tub, just used the disconnect, and tested
the GFI now and then. It was a pretty cool design. The tub's
electronics used the GFI as a "trip" to shut down in case of
overtemperature, etc, etc.,