JSON sent:
{"app_id":"32377c7c-cceb-4b6f-bba9-051aa27f3017","included_segments":["Elite"],"data":{"foo":"bar"},"contents":{"en":"alert message"},"headings":{"en":"Title"}}

JSON received:
{"allresponses":"{\"errors\": [\"Access denied.  Please include an 'Authorization: ...' header with a valid API key (https:\/\/documentation.onesignal.com\/docs\/accounts-and-keys).\"]}\n"}