Create upload

Uploads one file as multipart/form-data without a post and returns an upload_token. Pass it as a media item (media[].upload_token) to POST /posts, POST /posts/batch or PUT /posts/{post}, or to POST /posts/{post}/media/from-upload, before expires_at. A token is spent by the first post that takes it; to put the same file on another post, pass that post's media[].id. Unused uploads are deleted after 24 hours. Accepted files: JPEG, PNG, GIF and WebP images (HEIC and HEIF too when the server can convert them, stored as JPEG), MP4 and MOV videos, and PDF documents. Size caps: 10 MB per image (and at most about 67 megapixels, 8192 × 8192 pixels in total), 1 GB per video, 100 MB per PDF. Each network enforces its own, usually smaller, caps when the post is scheduled or published (GET /content-types).