Twilio Autopilot Custom and Dynamic on_failure message on validation failure

Question

In Twilio Autopilot, I want to validate user input. In this case order_number. Assume order_number can be anything between 8-12 characters. I have a webhook for validation. I want to let the user know why the validation failed if they entered an order number that was lt 8 or gt 12 characters, or if the order_number doesn't exists in our db.

My webhook returns { valid: true } or { valid: false } based on success or failure of validation.

My goal is to customize my failure message based on what validation failed. Is there a seamless way to achieve that ?

{
  collect: {
    name: 'collect_order_number',
    questions: [
      {
        question: 'Can I have your order number ?',
        name: 'order_number',
        type: 'Twilio.ALPHANUMERIC',
        validate: {
          on_failure: {
            messages: [  # How to customize this based on webhook validation ?
              { say: 'Order number too short' }, 
              { say: 'Order number too long' },
              { say: 'Could not find order number' },
            ],
            repeat_question: true,
          },
          webhook: {
            url: `https://<www.domain.com>/autopilot/validate_field`,
            method: 'POST',
          },
          on_success: {
            say: 'Great! got your order number',
          }
        }
      },
      { ... more questions }
    ]
  }
}