"non-mandatory-script-verify-flag" is replaced with "mempool-script-verify-flag-failed" See: https://github.com/bitcoin/bitcoin/pull/33050/ Should change here: https://github.com/btcsuite/btcd/blob/baebb836c2d4692da3de3b0d437f4da6ce915546/rpcclient/errors.go#L334-L335