That error usually means that there’s nothing to load from the file – either because there’s nothing in there, or because no example of the correct format was found (for instance, if none of the records have a text).
In your example, you’re loading in a file reviews.txt with the CSV loader – are you sure that’s correct? And did you have a look at the README and checked whether your data has the correct format? For CSV, the text should be available in a column “text” or “Text”. For TXT, each text should be on a new line. And for JSON or JSONL, each entry should have a key "text". You can find examples of this in your PRODIGY_README.html.