If you want to change default messages in woocommerce than you have to write below code in functions.php
function sagepay_woocommerce_add_error( $error ) {
if( ‘SagePay Direct – Card number required.’ == $error ) {
$error = ‘Card number required.’;
} else if( ‘SagePay Direct – Fullname required.’ == $error ) {
$error = ‘Fullname required.’;
} else if( ‘SagePay Direct – CV2 required.’ == $error ) {
$error = ‘CV2 required.’;
}
return $error;
}
add_filter( ‘woocommerce_add_error’, ‘sagepay_woocommerce_add_error’ );