How can we offer client to pay 50% when booking versus 100%

When the form takes the Client to Paypal it charges 100%,  How can we make sure it only applies 50% at this time?

You can work this out with coupon codes, please check this guide to learn how to set them up: https://www.jotform.com/help/233-How-To-Add-Coupon-Code-in-the-Payment-Form 

Let us know if you need more help, we will be glad to assist you.