If the form is pre-populated with values, this is because it has been previously used. In a production scenario, this form would be empty and require user input as a new payment authorisation session would be generated during each session.
Once the form has been submitted successfully, PostMessage ""asp--exit-screen"" is emitted from the iframe and the user is redirected to the next step.
Consideration is required as to how we handle 'More than one person is required to authorise Direct Debits' as this is not handled in PostMessage events
See Asperato iframe documentation for further info.