How do I stop a contact that is already enrolled or waiting to send?

Remove that person from every prospect list and every manual tag the flow targets. Do this on the contact in Contacts, or on the contact pane in Inbox. If they remain on any targeted list or tag, the flow keeps them.

The next send is then blocked. That includes a first action waiting for a daily slot or send window, and a later step after Connection sent or Message sent. The contact stays on Planned actions until that time. When it arrives, the send does not go out and the run pauses. Putting them back on a targeted list or tag does not resume that run. A connection request or message already delivered on LinkedIn stays there.

To stop every contact on the flow and clear scheduled steps now, open the agent and choose Set as inactive. Set as active puts those contacts back on the schedule. Console has no Unenroll button for one contact. If a scheduled step needs to leave Planned actions before it comes due, contact SMOC. After that removal, keep the contact off the flow’s lists and tags, or the next enrollment pass can schedule them again.