This was previously answered by Miquel Palet who said: You need to provide a public image URL — we don’t accept raw bytes/base64. Upload the file first (e.g., POST /api/v1/media or your CDN) and send the returned URL in mediaItems. Google Drive’s webContentLink usually needs auth; if you use Drive, make the file public and use: https://drive.google.com/uc?export=download&id=FILE_ID. You can find that answer here: https://appsumo.com/products/late/questions/image-post-1419738/