Custom fee rate (in base units) per kilobyte (or virtual kilobyte). For example, satoshis per kvByte.
If the feeRate is less than the minimum required network fee, then the minimum fee applies. For example, 1000 sat/kvByte, a flat 1000 microAlgos, or a flat 10 drops of xrp. For XRP, the actual fee is usually 4.5 times the open ledger fee.
Note: The feeRate overrides the maxFeeRate and minFeeRate.