No Vin Detected (HP Tuner)

I have a 1996 GMC Sierra. When I go to read vehicle window pops up with add vin number or continue with out. Any help on what I’m doing wrong or why it does that?

thank you

You're doing nothing wrong. You can enter the vehicles VIN number, usually found at the base of the windsreen, which will serve as a reference and, possibly, allow the HP Tuner to check the OEM parameters and equipment fitted.

If you don't wish to do so, just continue without entering it.