How to use the @zilliqa-js/core.RPCMethod.GetLatestTxBlock function in @zilliqa-js/core

private async getBlockNumber(): Promise {
    try {
      const res: RPCResponse = await this.provider.send(
        RPCMethod.GetLatestTxBlock,
      );
      if (res.error === undefined && res.result.header.BlockNum) {
        // if blockNumber is too high, we use BN to be safer
        return new BN(res.result.header.BlockNum);
      } else {
        throw new Error('Can not get latest BlockNumber');
      }
    } catch (error) {
      throw error;
    }
  }

getLatestTxBlock(): Promise> {
    return this.provider.send(RPCMethod.GetLatestTxBlock);
  }