Events will be POSTed to your callback URLs. There are two kinds of callbacks that can be defined.
Callback Response Format
The default format for messages sent to your callbacks is a multipart ('form/multipart') POST request, with the message details in a POST field named 'json'.
The Java SDK includes an event parsing class, and you can access this field in the $_POST array on PHP. For other platforms, either a library function, such as cgi.parse_multipart (for python) or ActionDispatch::Http::UploadedFile for Rails, or third party options, such as multer for node, may be useful.