Hi @MauG
If the file can be downloaded via the browser, it could be the format in your file.
Recommendation is pretty strict on the file structure, which can be a bit of hazzle the first time. Ensure you download the template and stick to that. Ensure you have 19 columns (even if you don't use them all), and even if you don't use the 'out of the box'-ones, keep them in the file and in the order and just have a space as value.
If you're using excel to save the file, be aware that it might screw up the format - I learned the hard way and it took me 3 days to realize. So I'm always using a text editor now when validating the files.
Let me know how it goes.