Review on 🔌 Leisure RV 125/250V 50 AMP Power Plug Twist Lock Inlet with 3 Stainless Steel Pins - White/Black (White) by Sheppard Priest

I bought this socket together with the 50A RV power cord (https://www.amazon.com/gp/product/B079ZBJM29 /ref=oh_aui_detailpage_o00_s00 ? ie= UTF8&psc=1) and a converter from 50A to 20A (https://www.amazon.com/gp/product/B00HRHWHNW/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1). All three arrived together but two of the cords have four pins and the entrance only has three. I've looked around the Revain and there are tons of 3-pin inputs and lots of 4-pin cables. How do people deal with this? Sorry if I don't understand, this is my first electrical project.