APEX_web_service.g_request_headers(1).name := 'Content-Type';
APEX_web_service.g_request_headers(1).value := 'application/json';
APEX_web_service.g_request_headers(2).name := 'authorization';
APEX_web_service.g_request_headers(2).value := 'key=your key goes here';
l_clob := APEX_web_service.make_rest_request(
p_url => 'https://fcm.googleapis.com/fcm/send',
p_http_method => 'POST',
p_parm_name => APEX_util.string_to_table('notification:to:data'),
p_parm_value => APEX_util.string_to_table('{"title": "Patriots vs Rams","text": "5 to 1"}:"your key":{"message":"New Ticket has been assigned to you"}')