Here is a visual.
Full size it to read the print.
Make sure to use correct wire size for load, distance and location conditions.
Copper is not cheap, neither is saftey it has a heaftier price.
Find the name on hot tub "control pack", not hot tub "Brand" Some may only be three wire hook up to control pack. (not to often, but still out there)
If it is a used spa it could have had its pack replaced with a different brand than what Mfg. origonally installed.
Some control pack Mfgs. have info online. (ie. Balboa)

**If there is any 120V devices on your spa, like the blower or light system, it needs a neutral. Some instructions manuals can be confusing.