How about trying it through the panel?
Go to the website then head over to the server you are trying to download the world on, head over to "World" option on the header section, click on "Upload world" which will be roughly the 4th option then you can select the world you are trying to upload.
It'll probably look like this. https://gyazo.com/cae096f6d11b926fda2acc4ede2c3573