Update texts

resources/lang/en/texts.php

@@ -4177,6 +4177,7 @@ $LANG = array(
      'migration_auth_label' => 'Let\'s continue by authenticating.',
      'api_secret' => 'API secret',
      'migration_api_secret_notice' => 'You can find API_SECRET in the .env file or Invoice Ninja v5. If property is missing, leave field blank.',
+     'promo_code' => 'Promo code',
 );
 
 return $LANG;