500 error

The issue was not related to the plugin, you had a custom code in your functions.php file which was incorrect and caused the error. I made a correction to it, now it is going to be fine. For reference, this is the correct code:

// Replace search phrases
add_filter('asp_search_phrase_before_cleaning', 'asp_replace_characters', 10, 1);
add_filter('asp_query_args', 'asp_replace_characters', 10, 1);
function asp_replace_characters( $s ) {
	$before_strings = array(
		"landc" => "land c", //land cruiser
		"brakes" => "brake",
		"rangero" => "range ro", //range rover
		"landr" => "land r", //land rover
		"towb" => "tow b", //towbar
		"bellh" => "bell h", //bellhousing
		"extractor" => "header",
		"pickup" => "ute",
		"hood" => "bonnet",
		"mfg12" => "mfk12",
		"brake disc" => "brake rotor",
		"adapte" => "adapto",
		"centref" => "centerf",
		"hydrob" => "hydro b"
	);
	
	foreach($before_strings as $key => $value){
		if ( is_array($s) ) {
			$s['s'] = str_replace($key, $value, $s['s']);
		} else {
			$s = str_replace($key, $value, $s);
		}
	};
	
  	return $s; 
}