The settxfee RPC sets the transaction fee per kilobyte paid by transactions created by this wallet.
settxfee amount
*bitcoin-cli help settxfee
settxfee amount Set the transaction fee per kB for this wallet. Overrides the global -paytxfee command line parameter. Arguments: 1. amount (numeric or string, required) The transaction fee in BTC/kB Result true|false (boolean) Returns true if successful Examples: > bitcoin-cli settxfee 0.00001 > curl --user myusername --data-binary '{"jsonrpc": "1.0", "id":"curltest", "method": "settxfee", "params": [0.00001] }' -H 'content-type: text/plain;' http://127.0.0.1:8332/