Woobewoo product filter undefined error

after the latest update I am suddenly seeing the below on all the shop pages

Warning: Use of undefined constant WPF_FREE_REQUIRES – assumed ‘WPF_FREE_REQUIRES’ (this will throw an Error in a future version of PHP) in /homepages/15/d836038036/htdocs/clickandbuilds/ParifyLighting/wp-content/plugins/woo-product-filter/modules/woofilters/mod.php on line 168

line 168 has the below code

if ( version_compare( '1.4.9', WPF_FREE_REQUIRES, '>' ) ) {
					DispatcherWpf::doAction( 'addDefaultFilterData', $filterId, $settings );
				} else {
					$preselects = DispatcherWpf::applyFilters( 'addDefaultFilterData', $preselects, $filterId, $settings );
				}
			}
			$this->preFilters[$filterId] = $preselects;
		}
		return $this->preFilters[$filterId];
	}

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