Aspose cloud REST API exception

http://api.aspose.com/v1.1/storage/file/{*path}

This API works. Then I am tries to merge these documents into one.

http://api.aspose.com/v1.1/pdf/MergingResult.pdf/merge
I am getting exception 
{"Message":"Error 'AmazonS3 exception: The specified key does not exist.', Path '[Ljava.lang.Object;@3974a835'"}

Requests are sent from google apps script. For both methods I use the same SID and appKey.