Hey Max,
Technical questions like this should be posted on
Stack Overflow and tagged as Shopify.
For the curl you pasted, the url looks malformed. Specifically, check the 'producti.d.xml' portion at the end and make sure that you're using the myshopify version of the url.
Additionally, it would help if you could post the contents of the xml file you're trying to upload as well as the error you're receiving. Thanks!
-David Underwood
Developer Advocate, Shopify