Business Logic Vulnerability. Simple Case.
Business logic vulnerability is an error in the application logic that can be exploited by the user and it can be hard to detect because generally, those have to be found manually.
The simple case would be finding a logic flaw in a chatbot and getting an unauthorized discount. While getting an unauthorized discount is not a critical issue, issues like this can be critical to the business’s functionality. Manual testing of the entire application is required to find and mitigate flaws like this to prevent possibility of the abuse.