You cannot upload a sound file through API on OBD platform. However, you can play the file from the panel. To do so, follow the API below:
//obd.solutionsinfini.com/api/v1/?api_key=yourapikeyhere&method=voice.call&play=3XXXX1.sound&numbers=9xxxxxxxxx&format=xml
To know more about our API, visit https://developers.kaleyra.com/