bitcoin/doc/release-notes-31278.md

RPC and Startup Option

The -paytxfee startup option and the settxfee RPC are now deprecated and will be removed in Bitcoin Core 31.0. They allowed the user to set a static fee rate for wallet transactions, which could potentially lead to overpaying or underpaying. Users should instead rely on fee estimation or specify a fee rate per transaction using the fee_rate argument in RPCs such as fundrawtransaction, sendtoaddress, send, sendall, and sendmany. (#31278)