This should be
echo json_encode([ "status" => "ok", "data" => [ [ "franchisor_no" => "1210110080", "franchisor_status" => "exception", "events_list" => [ [ "date" => "30-07-2023", "status" => "exception", "description" => "optional", "code" => "optional", "location" => "optional", "raw_event" => "mandatory" ], ], ], ]]);
You did not call the json_encode() function. You just put an equal sign in front of it.