Whatsapp API does not honor "context" with message_id when replying to media messages. but does honor it when replying to text message. so the code below does not work. the message is send as a normal message and not as a reply.
{ "messaging_product": "whatsapp", "recipient_type": "individual", "to": 1234567891, "type": "audio", "audio": { "link": "https://my_url/my_download_link" }, "context": { "message_id": "message_I_am_replying_to_ID" } }