When a user generates a dynamic preview and receives the error "Can't show a preview because you haven't set a default creative or your applied filters don't match any feed rows," what first step should be taken to troubleshoot the error?

The error message explicitly states, "your applied filters don't match any feed rows." This directly points to an issue with the filtering parameters. The first troubleshooting step should be to verify that the filters selected in the dynamic preview panel correctly correspond to data within your feed. Incorrect or overly restrictive filters would prevent any creative from being displayed, leading to this error. Retransforming or re-uploading the feed would not address incorrect filter settings. While confirming the feed is complete is good practice, the error message specifically indicates a filter mismatch, not a feed integrity issue.