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``

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.')