Hello cannonmc!
Well, I have created a new folder / directory "Transmission Uploads" (where the mp4 is) - besides my "Transmission Downloads" folder. So upload and download should not interfere.
I did quite a lot of search in forums. Could it be, that my upload is not "approved" yet (after 4 or 5 hours)?
Sorry, I'm very new to this …
Thank you for your advice anyway!
Boris / vollbart71