Hey @meave37! Please note that the file uploaded to the incentive email won't be downloaded until the subscriber opens the incentive email in their inbox and then clicks the button in that email.
Since you mentioned a success message, it sounds like you might be referring to just after the subscriber submitted the form on your site. They won't receive the incentive download at that point — they get that from the incentive email in their inbox :)
We actually have a video tutorial that covers this whole process in our Lunch & Learn Video Series114! That series is really helpful to gain an understanding of ConvertKit; however, you don't have to watch all of the videos if you don't feel you need them — feel free to skip to the one titled 'Setting Up The Incentive (Confirmation) Email' for that specific guide ☺️