Thanks for the info!
I found out why I didn't get the error message in my custom script.
The Twilio custom script had a typo in the invalid code line.
It was `facesMessages.add(facesMessage.SEVERITY_ERROR, "Incorrect Twilio code, please try again.")`
It should be `facesMessages.add(FacesMessage.SEVERITY_ERROR, "Incorrect Twilio code, please try again.")`
Capital `F` for the FacesMessage