def _request_check(input_json):
    """Check if the request json is valid"""
    if input_json is None or not isinstance(input_json, dict):
        return 'Can not parse the input json data - {}'.format(input_json)
    try:
        c = input_json['context']
        qa = input_json['qas'][0]
        qid = qa['qid']
        q = qa['question']
    except KeyError as e:
        return 'Invalid request, key "{}" not found'.format(e)
    return 'OK'