n8n AI agent workflow looped invoice sending and billed client 91 times in one night

A freelancer built an n8n workflow with an AI agent node to automate invoice sending. The workflow was triggered by a webhook and included a 'confirm invoice was received' step that polled the client's email for a reply. Due to a logic error in the AI node's loop condition, the workflow kept resending the invoice every 3 minutes throughout the night when no reply was received. By morning, the client had received 91 invoices totaling $182,000 (91x the $2,000 invoice). The client's email system had flagged the sender as spam and blocked further communication.