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Not an expert on spa codes, but I believe liquid tight (are you using non metallic?) Needs to be limited to 6 feet or less in length which is why you typically see PVC for most of branch run and then short flexible connection
Most tubs require 6/3 to your shut off / GFCI... And then you can your two hots and an insulated ground to the tub... Any wire in conduit should be THHN.Hope that helps!