feeRate
Set a custom fee rate.
This method sets the mining fee paid by the transaction as a rate on its size. This means that the total fee paid is equal to fee_rate times the size of the transaction. Default is 1 sat/vB in accordance with Bitcoin Core’s default relay policy.
Note that this is really a minimum feerate – it’s possible to overshoot it slightly since adding a change output to drain the remaining excess might not be viable.