Although I have not found the answer to this, I found an alternative way to achieve a subscription, through the Instagram API console.
You need to put
- In the Query the verify_token, client_id, client_secret
- In the Body, inside the Text something like this (or the equivalent for your subscription):
aspect=media;callback_url=http://54.77.253.34/instagram/InstagramServlet;object=location;object_id=18945195;
I got the hub.challenge=**** in my tomcat logs and therefore confirmed that the subscription was made.
Still, no idea as to why it is not working through the curl.
