script.js

async function watermarkJob(source, watermark, token, clientId) {
	let body = {
		'inputDocumentAssetID': source.assetID,
		'watermarkDocumentAssetID': watermark.assetID
	}

	let resp = await fetch(REST_API + 'operation/addwatermark', {
		method: 'POST', 
		headers: {
			'Authorization':`Bearer ${token}`, 
			'X-API-KEY':clientId,
			'Content-Type':'application/json'
		},
		body:JSON.stringify(body)
	});

	return resp.headers.get('location');

}