Recently installed a hot but. All wiring is correct, and has been rechecked. When the breaker is flipped beaker on, it immediately trips. My electrican says there is no direct short, however there is enough resistance to cause the breaker to trip. Looking for someone thoughts on what is causing this, and how to correct. Thank you for your assistance.

New or used hot tub?

First guess would be the GFCI breaker is wired incorrectly (regardless of what the first electrician says... they're frequently WRONG).

First, get a new electrician, GFI devices do not trip because of resistance.

Could be a defective GFI CB, could be wired wrong, and could be something in the tub to cause a ground fault.

A good electrician that understands GFI devices and hot tubs should be able to troubleshoot this.