Automatic rollback
If an endpoint's logic fails, or deliberately reaches an Error Response block, after it already made one or more Database Query writes (an insert, update, or delete), those writes are automatically undone before the error is returned to the caller, an insert is deleted, an update is restored to its prior value, a delete is re-inserted. Reaching a normal Response block never triggers this, that's your endpoint's own signal that things succeeded.
This only covers this project's own data. A side effect from a Call External API block, an email sent, a charge made elsewhere, is never undone, there's no way for us to reverse something that happened on a service outside this app.
Seeing exactly what a request sent
Turn on Log details in an endpoint's builder header to capture the full request and response (query, body, status) for its most recent 50 calls, viewable in the Recent Requests panel. It's off by default, and worth leaving off for an endpoint that might receive sensitive data you don't want stored, even briefly.