It is a common misconception that when a prospect is picked up by another agency, they are considered a lost listing; however, until prospects have been appraised, they are not technically considered as a lost listing. As such, there is no option to mark a prospect as a lost listing.
If a prospect is no longer proceeding with your agency, you can update its status in the property timeline. To do this, select either "listed with other agent" or "not proceeding" from the statuses dropdown:
