Attaches images/video/3D to an existing product via productUpdate's media argument (productCreateMedia is deprecated as of API 2026-04). Body: { media: CreateMediaInput[] } — each entry { originalSource, alt?, mediaContentType }; originalSource must be a publicly reachable URL, Shopify fetches it server-side (no binary upload).

• Write — changes a live ad account immediately; needs a write-scoped token.

Uploading a file. As well as the JSON body above, this route accepts multipart/form-data with a file part (other parts ride along as platform fields), or file_base64 inside the JSON body — raw base64 or a data: URI, plus optional file_name/file_type. file_base64 is the only way an MCP caller can send bytes. mediaContentType is derived from the file and must not be passed on that path. JPEG/PNG/GIF/WebP up to 10MB; MP4/MOV/WebM up to 64MB. Above that the request is rejected by the ingress with a plain 413 (an HTML error page, not this API's JSON envelope) — the ceiling is our request-size limit, not the vendor's. A rejected type or size is 400 FILE_UPLOAD_INVALID; unavailable storage is 503 FILE_STAGING_FAILED (retry the identical request).