Hi,
these samples are bit outdated. You may review my pastebins in following post: Spreadshirt Forum Login
Despite of that, api will change in some months, as the endpoints are currently for old partner area only - so for accounts created before October 2016. Newer aren’t yet officially supported by api.
If you review my samples, you should be able to upload and place a design (for old Accounts).
Best
Thimo