diff --git a/lib/Application/Reservation/Validation/AccessoryResourceRule.php b/lib/Application/Reservation/Validation/AccessoryResourceRule.php
index cc358b2cc..46cd860c4 100644
--- a/lib/Application/Reservation/Validation/AccessoryResourceRule.php
+++ b/lib/Application/Reservation/Validation/AccessoryResourceRule.php
@@ -14,59 +14,88 @@ class AccessoryResourceRule implements IReservationValidationRule
      */
     private $strings;
 
+    /**
+     * Constructor for initializing dependencies
+     *
+     * @param IAccessoryRepository $accessoryRepository
+     */
     public function __construct(IAccessoryRepository $accessoryRepository)
     {
         $this->accessoryRepository = $accessoryRepository;
         $this->strings = Resources::GetInstance();
     }
 
+    /**
+     * Validates reservations for accessory-resource rules
+     *
+     * @param $reservationSeries
+     * @param $retryParameters
+     * @return ReservationRuleResult
+     */
     public function Validate($reservationSeries, $retryParameters)
     {
         $errors = [];
 
-        /** @var ReservationAccessory[] $bookedAccessories */
+        // Step 1: Collect booked accessories
         $bookedAccessories = [];
-
         foreach ($reservationSeries->Accessories() as $accessory) {
             $bookedAccessories[$accessory->AccessoryId] = $accessory;
         }
 
+        // Step 2: Load all accessories and create associations
         $accessories = $this->accessoryRepository->LoadAll();
-
         $association = $this->GetResourcesAndRequiredAccessories($accessories);
-
         $bookedResourceIds = $reservationSeries->AllResourceIds();
 
+        // Step 3: Find invalid accessory-resource associations
         $badAccessories = $association->GetAccessoriesThatCannotBeBookedWithGivenResources($bookedAccessories, $bookedResourceIds);
 
         foreach ($badAccessories as $accessoryName) {
             $errors[] = $this->strings->GetString('AccessoryResourceAssociationErrorMessage', $accessoryName);
         }
 
+        // Step 4: Ensure all accessories have a QuantityReserved value (even if not booked)
+        foreach ($accessories as $accessory) {
+            if (!isset($bookedAccessories[$accessory->GetId()])) {
+                $bookedAccessories[$accessory->GetId()] = (object) ['QuantityReserved' => 0];
+            }
+        }
+
+        // Step 5: Validate min and max quantities for resources and accessories
         foreach ($reservationSeries->AllResources() as $resource) {
             $resourceId = $resource->GetResourceId();
             if ($association->ContainsResource($resourceId)) {
-                /** @var Accessory[] $resourceAccessories */
                 $resourceAccessories = $association->GetResourceAccessories($resourceId);
                 foreach ($resourceAccessories as $accessory) {
                     $accessoryId = $accessory->GetId();
 
-                    $resource = $accessory->GetResource($resourceId);
-                    if (!empty($resource->MinQuantity) && $bookedAccessories[$accessoryId]->QuantityReserved < $resource->MinQuantity) {
-                        $errors[] = $this->strings->GetString('AccessoryMinQuantityErrorMessage', [$resource->MinQuantity, $accessory->GetName()]);
-                    }
-
-                    if (!empty($resource->MaxQuantity) && $bookedAccessories[$accessoryId]->QuantityReserved > $resource->MaxQuantity) {
-                        $errors[] = $this->strings->GetString('AccessoryMaxQuantityErrorMessage', [$resource->MaxQuantity, $accessory->GetName()]);
+                    if (isset($bookedAccessories[$accessoryId]) && $bookedAccessories[$accessoryId] !== null) {
+                        $resource = $accessory->GetResource($resourceId);
+
+                        // Validate minimum quantity
+                        if (!is_null($resource->MinQuantity) && $bookedAccessories[$accessoryId]->QuantityReserved < $resource->MinQuantity) {
+                            $errors[] = $this->strings->GetString('AccessoryMinQuantityErrorMessage', [$resource->MinQuantity, $accessory->GetName()]);
+                        }
+
+                        // Validate maximum quantity
+                        if (!is_null($resource->MaxQuantity) && $bookedAccessories[$accessoryId]->QuantityReserved > $resource->MaxQuantity) {
+                            $errors[] = $this->strings->GetString('AccessoryMaxQuantityErrorMessage', [$resource->MaxQuantity, $accessory->GetName()]);
+                        }
+                    } else {
+                        // Error for unbooked accessory
+                        $errors[] = $this->strings->GetString('AccessoryNotBookedErrorMessage', $accessory->GetName());
                     }
                 }
             }
         }
 
+        // Return validation result
         return new ReservationRuleResult(count($errors) == 0, implode("\n", $errors));
     }
 
     /**
+     * Builds relationships between resources and accessories
+     *
      * @param Accessory[] $accessories
      * @return ResourceAccessoryAssociation
      */
@@ -79,7 +108,6 @@ private function GetResourcesAndRequiredAccessories($accessories)
                 $association->AddRelationship($resource, $accessory);
             }
         }
-
         return $association;
     }
 }
@@ -92,6 +120,8 @@ class ResourceAccessoryAssociation
     private $accessories = [];
 
     /**
+     * Adds a relationship between a resource and an accessory
+     *
      * @param ResourceAccessory $resource
      * @param Accessory $accessory
      */
@@ -101,6 +131,8 @@ public function AddRelationship($resource, $accessory)
     }
 
     /**
+     * Checks if a resource exists in the association
+     *
      * @param int $resourceId
      * @return bool
      */
@@ -110,15 +142,19 @@ public function ContainsResource($resourceId)
     }
 
     /**
+     * Gets accessories associated with a resource
+     *
      * @param int $resourceId
      * @return Accessory[]
      */
     public function GetResourceAccessories($resourceId)
     {
-        return $this->resources[$resourceId];
+        return $this->resources[$resourceId] ?? [];
     }
 
     /**
+     * Adds an accessory to the association
+     *
      * @param Accessory $accessory
      */
     public function AddAccessory(Accessory $accessory)
@@ -127,6 +163,8 @@ public function AddAccessory(Accessory $accessory)
     }
 
     /**
+     * Identifies accessories that cannot be booked with the given resources
+     *
      * @param ReservationAccessory[] $bookedAccessories
      * @param int[] $bookedResourceIds
      * @return string[]
@@ -135,10 +173,8 @@ public function GetAccessoriesThatCannotBeBookedWithGivenResources($bookedAccess
     {
         $badAccessories = [];
 
-        $bookedAccessoryIds = [];
         foreach ($bookedAccessories as $accessory) {
             $accessoryId = $accessory->AccessoryId;
-            $bookedAccessoryIds[] = $accessoryId;
 
             if ($this->AccessoryNeedsARequiredResourceToBeBooked($accessoryId, $bookedResourceIds)) {
                 $badAccessories[] = $this->accessories[$accessoryId]->GetName();
@@ -148,6 +184,13 @@ public function GetAccessoriesThatCannotBeBookedWithGivenResources($bookedAccess
         return $badAccessories;
     }
 
+    /**
+     * Checks if an accessory requires a specific resource to be booked
+     *
+     * @param int $accessoryId
+     * @param int[] $bookedResourceIds
+     * @return bool
+     */
     private function AccessoryNeedsARequiredResourceToBeBooked($accessoryId, $bookedResourceIds)
     {
         $accessory = $this->accessories[$accessoryId];