web3.TransactionManager.DefaultGas = 210000; // Gas limit?
web3.TransactionManager.DefaultGasPrice = 10 * 1000000000; // Gas Price?
I have intended to set the gas price at 10Gwei.
Yes, your gas price is 10Gwei. But gas limit is 10 times higher than required for regular transaction without extra data. However if you do contract calls, then maybe it is low, some contracts ask for 300,000 gas limit.