Flips the item's completion state: an open item becomes completed, and a completed item becomes
open again. No request body is needed. Because it is a toggle, sending the same request twice
returns the item to where it started, so read the item's completed value first if you need a
particular end state.

Completing an item records the time and the user behind the token as completed_by; reopening it
clears both. Either change adds an entry to the job's activity log. Completing an item can also
start any automations your company has attached to it, and completing the last item of a stage
checklist can move the deal to its next stage.

The token's role only needs to allow viewing the job or lead the checklist belongs to.