diff --git a/apps/full-site-editing/full-site-editing-plugin/starter-page-templates/class-wp-rest-batch-controller.php b/apps/full-site-editing/full-site-editing-plugin/starter-page-templates/class-wp-rest-batch-controller.php
index 72e2592f1d7d5..e674491d7fdee 100644
--- a/apps/full-site-editing/full-site-editing-plugin/starter-page-templates/class-wp-rest-batch-controller.php
+++ b/apps/full-site-editing/full-site-editing-plugin/starter-page-templates/class-wp-rest-batch-controller.php
@@ -78,9 +78,9 @@ public function handle_batch_requests( $request ) {
 
 		// Foreach request specified in the requests param, run the endpoint.
 		foreach ( $request['requests'] as $request_params ) {
-			$response     = $this->handle_request( $request_params );
-			$key          = $request_params['method'] . ' ' . $request_params['route'];
-			$data[ $key ] = $this->prepare_for_collection( $response );
+			$response       = $this->handle_request( $request_params );
+			$key            = $request_params['method'] . ' ' . $request_params['route'];
+			$data[ $key ][] = $this->prepare_for_collection( $response );
 		}
 
 		return rest_ensure_response( $data );
diff --git a/apps/full-site-editing/full-site-editing-plugin/starter-page-templates/class-wp-rest-sideload-image-controller.php b/apps/full-site-editing/full-site-editing-plugin/starter-page-templates/class-wp-rest-sideload-image-controller.php
index 01f97d99c39f9..6bf90eddb5067 100644
--- a/apps/full-site-editing/full-site-editing-plugin/starter-page-templates/class-wp-rest-sideload-image-controller.php
+++ b/apps/full-site-editing/full-site-editing-plugin/starter-page-templates/class-wp-rest-sideload-image-controller.php
@@ -57,7 +57,7 @@ public function register_routes() {
 	 * @return WP_Error|WP_REST_Response Response object on success, WP_Error object on failure.
 	 */
 	public function create_item( $request ) {
-		if ( in_array( get_post_type( $request->get_param( 'post_id' ) ), [ 'revision', 'attachment' ], true ) ) {
+		if ( ! empty( $request['post_id'] ) && in_array( get_post_type( $request['post_id'] ), [ 'revision', 'attachment' ], true ) ) {
 			return new WP_Error( 'rest_invalid_param', __( 'Invalid parent type.' ), [ 'status' => 400 ] );
 		}
 
diff --git a/apps/full-site-editing/full-site-editing-plugin/starter-page-templates/page-template-modal/utils/ensure-assets.js b/apps/full-site-editing/full-site-editing-plugin/starter-page-templates/page-template-modal/utils/ensure-assets.js
index 98627c75d5967..02d04591b176b 100644
--- a/apps/full-site-editing/full-site-editing-plugin/starter-page-templates/page-template-modal/utils/ensure-assets.js
+++ b/apps/full-site-editing/full-site-editing-plugin/starter-page-templates/page-template-modal/utils/ensure-assets.js
@@ -3,6 +3,12 @@
  */
 import { reduce, isEmpty, forEach, set } from 'lodash';
 
+/**
+ * WordPress dependencies
+ */
+import apiFetch from '@wordpress/api-fetch';
+import { addQueryArgs } from '@wordpress/url';
+
 /**
  * A full asset URL.
  * @typedef {String} URL
@@ -133,28 +139,33 @@ const findAssetsInBlock = ( session, block ) => {
  * @returns {Promise} Promise that resoves into an object with URLs as keys and fetch results as values.
  */
 const fetchAssets = async assets => {
-	return new Promise( resolve => {
-		// Simulate API call delay.
-		setTimeout( () => {
-			// TODO: Get this from API response.
-			const mockImage = {
-				id: 66,
-				url:
-					'http://test.local/wp-content/uploads/2019/07/Screenshot-2019-07-16-at-17.30.52-1021x1024.png',
-			};
-
-			resolve(
-				reduce(
-					assets,
-					( fetched, asset ) => ( {
-						...fetched,
-						[ asset.url ]: mockImage,
-					} ),
-					{}
-				)
-			);
-		}, 1000 );
+	const requests = [];
+
+	forEach( assets, ( { url } ) => {
+		requests.push( {
+			method: 'POST',
+			route: '/fse/v1/sideload/image',
+			params: { url },
+		} );
 	} );
+
+	return await apiFetch( {
+		method: 'POST',
+		path: addQueryArgs( '/fse/v1/batch', { requests } ),
+	} ).then( response =>
+		reduce(
+			assets,
+			( fetched, asset ) => {
+				const { id, source_url } = response[ 'POST /fse/v1/sideload/image' ].shift();
+
+				return {
+					...fetched,
+					[ asset.url ]: { id, url: source_url },
+				};
+			},
+			{}
+		)
+	);
 };
 
 /**
diff --git a/apps/full-site-editing/package.json b/apps/full-site-editing/package.json
index 0e98ff492de1e..acb9e0883ee58 100644
--- a/apps/full-site-editing/package.json
+++ b/apps/full-site-editing/package.json
@@ -29,7 +29,7 @@
 		"build": "rimraf dist && npm-run-all --parallel build:*"
 	},
 	"dependencies": {
-		"@wordpress/api-fetch": "^3.1.2",
+		"@wordpress/api-fetch": "^3.3.0",
 		"@wordpress/blocks": "^6.2.3",
 		"@wordpress/components": "^7.3.0",
 		"@wordpress/compose": "^3.2.0",