As a Club Admin - Require A Program Prerequisite/Require Invitation
GotSport's Program Registration software offers a tool that requires a previous program registration to be Completed and Approved before a player can register for a specific program. If the player did not register for this prerequisite program, they will not be able to register for this specific program. The below instructions will demonstrate how to utilize this tool.
Instructions
Step 1:
Build the program just as any other program registration
Here is an article that details creating a program registration: https://gotsport.zendesk.com/hc/en-us/articles/360022257254-8-Steps-to-Create-a-Program-Registration
Step 2:
Selecting the Prerequisite
Under the Program Setup, Scroll down and check the Invitation Required box.
Then, select the appropriate program prerequisite (The player will need to have been registered for this program), and click Save at the bottom.

This feature is often used in conjunction with a club's Tryouts, the Tryout being the Invitation Program or program prerequisite.
Next Step:
As Club Admin- How to Send and Monitor Registration Invitations After a Try Out