Hey Luis, you don't have to create the part first. At first I didn't like this design, but later saw a benefit and a niche. Cin7 is designed to work with EDI and hundreds of integrations. Dropdown fields make integrations difficult. There is a catch though. If you don't go to the product screen and create the product first, it won't show up in stock after you receive it. Which for random misc products, that makes perfect sense.
