You can try this way
And everyone has tested this example and works?
I tried this and got a error "nofile" - please tell me, where is my fail?
https://<HOST>/<MOODLE>/webservice/rest/server.php?moodlewsrestformat=json&wstoken=<TOKEN FROM OUR WS USER>&wsfunction=core_files_upload&contextlevel=user&instanceid=<USER ID>&component=user&filearea=draft&itemid=0&filepath=/&filename=test&filecontent=hello
Don't pass the parameter itemid and then try
The Parameter itemid is required and must be a int value
Can you tell me how you are calling the service?
Are you using POST method?