Merge pull request #4651 from nextcloud/backport/4648/stable1.9

[stable1.9] Add missing route for zip download

appinfo/routes.php

@@ -119,6 +119,11 @@ return [
 			'url' => '/api/messages/{id}/attachment/{attachmentId}',
 			'verb' => 'GET'
 		],
+		[
+			'name' => 'messages#downloadAttachments',
+			'url' => '/api/messages/{id}/attachments',
+			'verb' => 'GET'
+		],
 		[
 			'name' => 'messages#saveAttachment',
 			'url' => '/api/messages/{id}/attachment/{attachmentId}',