Complete a media upload session

{  "data": {    "asset_id": "8f5f3f18-3cf7-4aa8-a0ea-6fd204d4c4f1",    "status": "completed",    "filename": "launch-card.png",    "content_type": "image/png",    "size_bytes": 481233,    "upload_url": null,    "upload_method": null,    "upload_headers": {},    "expires_at": null,    "url": "https://cdn.postmantis.com/media/launch-card.png",    "created_at": "2026-03-29T09:30:00Z",    "completed_at": "2026-03-29T09:31:00Z"  }}

{  "type": "https://postmantis.com/problems/invalid-request",  "title": "Invalid request",  "status": 400,  "detail": "The request payload failed validation.",  "code": "invalid_request"}

{  "type": "https://postmantis.com/problems/unauthorized",  "title": "Unauthorized",  "status": 401,  "detail": "Missing or invalid API key.",  "code": "unauthorized"}

{  "type": "https://postmantis.com/problems/forbidden",  "title": "Forbidden",  "status": 403,  "detail": "The authenticated API key is not allowed to perform this action.",  "code": "forbidden"}

{  "type": "https://postmantis.com/problems/upload-not-found",  "title": "Upload not found",  "status": 404,  "detail": "Upload not found.",  "code": "upload_not_found"}

{  "type": "https://postmantis.com/problems/upload-not-ready",  "title": "Upload not ready",  "status": 409,  "detail": "Upload cannot be completed from its current state.",  "code": "upload_not_ready"}

{  "error": "Too Many Requests"}