Standard booth registration is only available with an online credit card transaction on the event's website. It is not available through Bookkeeping or with an offline payment type of cash or check. 

You can enter the booth registration offline in two ways
  1. Create a backend only registration type, and register them in Bookkeeping > Registration Entry. This will give the booth vendor their own fundraising page. 
  2. If the booth vendor does not need to fundraise within the event, enter them as an offline cash or check donation in Bookkeeping > Gift Entry