If you cannot select an option from the Checklist drop down, this means the user already has a checklist associated with them or the registered externally (see full description below). You can view their checklist in:
  1. onBoard > People Finder > select their name.
  2. Click on their Checklist tab.
  3. The checklist Name is in the top-left of the Checklist tab.User-added image

A parent has two ways to fill out the registration form, either through the external link provided when editing the registration, or they can go to their child's profile page and if there's a step for the registration in their checklist, they can click the Register button for the event while viewing their child's checklist. In the case that the registration is filled out through an external link, because it's not attached to a user profile, a checklist can't be selected to update.

If the registration was filled out through the candidate's profile, then when processing the registration, you will see the name of the assigned checklist in the checklist field. This means that their checklist will successfully update when the registration is processed.

Essentially, this field isn't so much a selection of the checklist you want to tie to a user, but a display of the already attached checklist, if there is one, to acknowledge that this checklist will be updated for the user.

This has been communicated to our Development team and an idea has been created for checklists to be able to be selected when processing an external registration: https://blackbaudk12.ideas.aha.io/ideas/K12OB-I-798