Agent error
An agent error in travel refers to when a travel agent (or agency) issues a ticket that doesn’t fully comply with the airline’s published fare rules.
For example, a passenger selects a discounted fare that requires tickets to be issued at least seven days before departure. The agent books the reservation on April 1 for travel on April 9, but doesn’t issue the ticket until April 6 (only three days before departure).
Because the ticket violates these rules, the airline considers it invalid and holds the agent financially responsible via an Agency Debit Memo (ADM), a monetary penalty notice.