Adds an event handler that runs when the CAPTCHA challenge is successfully completed.
Once the CAPTCHA challenge has been successfully completed by the user, the onVerified
callback is triggered and a CAPTCHA token is generated.
If the clickable element for triggering the submit or another restricted operation was disabled, enable it.
handler(): Promise<void> | void
The name of the function or
the function expression to run when the CAPTCHA is verified.