CreateUploadSession with creating a new file keep getting 404

Question

I'm currently trying to upload big file so first I want to create an upload session, using this POST request:

"/sites/{siteId}/drive/items/root:/{fileName}:/createUploadSession"

But by doing so I keep getting a 404 Not found. If I replace the url and add an itemId instead of the root:/{filename} for an already existing file it work fine and I get the correct response. Also when I upload a small file using /content instead of the /createUploadSession I have no issue. Do you have an idea why I keep getting 404 with the createUploadSession ? Thanks in advance,