Builds Indy request for setting fees for transactions in the ledger

    :param wallet_handle: wallet handle (created by open_wallet).
    :param submitter_did : (Option) DID of request sender
    :param payment_method: Payment method to use (for example, 'sov').
    :param fees_json: {
       txnType1: amount1,
       txnType2: amount2,
       .................
       txnTypeN: amountN,
     }
    :return: set_txn_fees_json: Indy request for setting fees for transactions in the ledger

async def build_set_txn_fees_req(wallet_handle: int,
                                 submitter_did: str,
                                 payment_method: str,
                                 fees_json: str) -> str:
    """
    Builds Indy request for setting fees for transactions in the ledger

    :param wallet_handle: wallet handle (created by open_wallet).
    :param submitter_did : (Option) DID of request sender
    :param payment_method: Payment method to use (for example, 'sov').
    :param fees_json: {
       txnType1: amount1,
       txnType2: amount2,
       .................
       txnTypeN: amountN,
     }
    :return: set_txn_fees_json: Indy request for setting fees for transactions in the ledger
    """

    logger = logging.getLogger(__name__)
    logger.debug("build_set_txn_fees_req: >>> wallet_handle: %r, submitter_did: %r, payment_method: %r, fees_json: %r",
                 wallet_handle,
                 submitter_did,
                 payment_method,
                 fees_json)

    if not hasattr(build_set_txn_fees_req, "cb"):
        logger.debug("build_set_txn_fees_req: Creating callback")
        build_set_txn_fees_req.cb = create_cb(CFUNCTYPE(None, c_int32, c_int32, c_char_p))

    c_wallet_handle = c_int32(wallet_handle)
    c_submitter_did = c_char_p(submitter_did.encode('utf-8')) if submitter_did is not None else None
    c_payment_method = c_char_p(payment_method.encode('utf-8'))
    c_fees_json = c_char_p(fees_json.encode('utf-8'))

    set_txn_fees_json = await do_call('indy_build_set_txn_fees_req',
                                      c_wallet_handle,
                                      c_submitter_did,
                                      c_payment_method,
                                      c_fees_json,
                                      build_set_txn_fees_req.cb)

    res = set_txn_fees_json.decode()
    logger.debug("build_set_txn_fees_req: <<< res: %r", res)
    return res