IPhone X and Verizon

I went to walmart buy an iPhone X and the people at the counter told me I had to buy the phone with a current Verizon’s plan. The problem is I don’t want the phone on a plan I just wanna but the 50$ prepaid Verizon cards every month but I wasn’t able to do that so my question is what do I need to do in order to buy the iPhone X and use the 50$ Verizon’s cards every month