registration form using unique code to validate approval

I have been trying to use the Ultimate Member registration form so a person who enters the correct administrative code that the company gives them (first field in the form url attached), they will be automatically approved and activated with a profile. And when a person enters an incorrect code, it should show an error message and stop registration. They are an employee trying to register and the company admin would email them the code to register.

The page I need help with: [log in to see the link]