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\":[\"Please include a case-sensitive header of Authorization: Basic \\u003cYOUR-REST-API-KEY-HERE\\u003e or Bearer token=\\\"\\u003cYOUR-REST-API-KEY-HERE\\u003e\\\" with a valid REST API key.\"],\"reference\":[\"https:\/\/documentation.onesignal.com\/docs\/accounts-and-keys#section-keys-ids\"]}"}