Add the following to your functions.php file.
function my_custom_error_messages() {
global $errors;
$err_codes = $errors->get_error_codes();
// Invalid username.
if ( in_array( 'invalid_username', $err_codes ) ) {
$error="<strong>ERROR</strong>: Custom Message Here";
}
// Incorrect password.
if ( in_array( 'incorrect_password', $err_codes ) ) {
$error="<strong>ERROR</strong>: Another Custom Message Here";
}
return $error;
}
add_filter( 'login_errors', 'my_custom_error_messages');
You can write a separate error message for each or combine the if statements if you only want one message. Like this.
if ( in_array( 'invalid_username', $err_codes ) || in_array( 'incorrect_password', $err_codes ) ) {
$error="<strong>ERROR</strong>: Custom Message Here";
}