@classmethod
def get_transaction_by_id(cls, txid):
    """Gets a raw transaction hex by its transaction id (txid).

        :param txid: The id of the transaction
        :type txid: ``str``
        :raises ConnectionError: If all API services fail.
        :rtype: ``string``
        """
    for api_call in cls.GET_TRANSACTION_BY_ID_MAIN:
        try:
            return api_call(txid)
        except cls.IGNORED_ERRORS:
            pass
    raise ConnectionError('All APIs are unreachable.')
