GoCardless - Create a bill under a pre-auth - Reponse

Question

I am creating a bill under a pre-auth using PHP from GoCardless. According to their documentation the response will return a bill object.

I have to check some special logic depending on the pass or failure of the payment.

Does anybody know what GoCardless will return if the payment was not successful? Is it false or the bill object with some status?

Thanks for the help!