diff --git a/src/ApiResource/Project/RewardClaimApiResource.php b/src/ApiResource/Project/RewardClaimApiResource.php
index f9c1d38..6ddfd97 100644
--- a/src/ApiResource/Project/RewardClaimApiResource.php
+++ b/src/ApiResource/Project/RewardClaimApiResource.php
@@ -4,10 +4,13 @@ namespace App\ApiResource\Project;
 
 use ApiPlatform\Doctrine\Orm\State\Options;
 use ApiPlatform\Metadata as API;
+use App\ApiResource\Gateway\ChargeApiResource;
 use App\ApiResource\User\UserApiResource;
 use App\Entity\Project\RewardClaim;
 use App\State\ApiResourceStateProvider;
 use App\State\Project\RewardClaimStateProcessor;
+use App\Validator\AvailableRewardUnits;
+use App\Validator\EnoughRewardCharge;
 use Symfony\Component\Validator\Constraints as Assert;
 
 /**
@@ -19,20 +22,28 @@ use Symfony\Component\Validator\Constraints as Assert;
     provider: ApiResourceStateProvider::class,
     processor: RewardClaimStateProcessor::class
 )]
+#[EnoughRewardCharge()]
 class RewardClaimApiResource
 {
     #[API\ApiProperty(identifier: true, writable: false)]
     public int $id;
 
-    /**
-     * The ProjectReward being claimed.
-     */
-    #[Assert\NotBlank()]
-    public RewardApiResource $reward;
-
     /**
      * The User claiming the ProjectReward.
      */
     #[API\ApiProperty(writable: false)]
     public UserApiResource $owner;
+
+    /**
+     * The GatewayCharge granting access to the ProjectReward.
+     */
+    #[Assert\NotBlank()]
+    public ChargeApiResource $charge;
+
+    /**
+     * The ProjectReward being claimed.
+     */
+    #[Assert\NotBlank()]
+    #[AvailableRewardUnits()]
+    public RewardApiResource $reward;
 }
diff --git a/src/Entity/Project/RewardClaim.php b/src/Entity/Project/RewardClaim.php
index feecac3..1707ea5 100644
--- a/src/Entity/Project/RewardClaim.php
+++ b/src/Entity/Project/RewardClaim.php
@@ -2,6 +2,7 @@
 
 namespace App\Entity\Project;
 
+use App\Entity\Gateway\Charge;
 use App\Entity\Interface\UserOwnedInterface;
 use App\Entity\Trait\UserOwnedTrait;
 use App\Entity\User\User;
@@ -22,6 +23,10 @@ class RewardClaim implements UserOwnedInterface
     #[ORM\Column]
     private ?int $id = null;
 
+    #[ORM\OneToOne(cascade: ['persist', 'remove'])]
+    #[ORM\JoinColumn(nullable: false)]
+    private ?Charge $charge = null;
+
     #[ORM\ManyToOne(inversedBy: 'claims')]
     #[ORM\JoinColumn(nullable: false)]
     private ?Reward $reward = null;
@@ -35,6 +40,18 @@ class RewardClaim implements UserOwnedInterface
         return $this->id;
     }
 
+    public function getCharge(): ?Charge
+    {
+        return $this->charge;
+    }
+
+    public function setCharge(Charge $charge): static
+    {
+        $this->charge = $charge;
+
+        return $this;
+    }
+
     public function getReward(): ?Reward
     {
         return $this->reward;
diff --git a/src/Service/Project/RewardService.php b/src/Service/Project/RewardService.php
deleted file mode 100644
index 131c1c7..0000000
--- a/src/Service/Project/RewardService.php
+++ /dev/null
@@ -1,34 +0,0 @@
-<?php
-
-namespace App\Service\Project;
-
-use App\Entity\Project\Reward;
-use App\Entity\Project\RewardClaim;
-
-class RewardService
-{
-    /**
-     * Processes a RewardClaim for the set Reward.
-     *
-     * @return RewardClaim The processed RewardClaim with updated Reward
-     */
-    public function processClaim(RewardClaim $claim): RewardClaim
-    {
-        $reward = $claim->getReward();
-
-        if (!$reward->hasUnits()) {
-            return $claim;
-        }
-
-        $available = $reward->getUnitsAvailable();
-
-        if ($available < 1) {
-            throw new \Exception('The claimed Reward has no units available');
-        }
-
-        $reward->addClaim($claim);
-        $reward->setUnitsAvailable($available - 1);
-
-        return $claim->setReward($reward);
-    }
-}
diff --git a/src/State/Project/RewardClaimStateProcessor.php b/src/State/Project/RewardClaimStateProcessor.php
index d3c5a94..ea47d14 100644
--- a/src/State/Project/RewardClaimStateProcessor.php
+++ b/src/State/Project/RewardClaimStateProcessor.php
@@ -8,7 +8,6 @@ use App\ApiResource\Project\RewardClaimApiResource;
 use App\Entity\Project\RewardClaim;
 use App\Mapping\AutoMapper;
 use App\Service\Auth\AuthService;
-use App\Service\Project\RewardService;
 use App\State\EntityStateProcessor;
 use Symfony\Component\Security\Core\Exception\AuthenticationException;
 
@@ -18,7 +17,6 @@ class RewardClaimStateProcessor implements ProcessorInterface
         private EntityStateProcessor $entityStateProcessor,
         private AutoMapper $autoMapper,
         private AuthService $authService,
-        private RewardService $rewardService,
     ) {}
 
     /**
@@ -41,7 +39,6 @@ class RewardClaimStateProcessor implements ProcessorInterface
             $claim->setOwner($owner);
         }
 
-        $claim = $this->rewardService->processClaim($claim);
         $claim = $this->entityStateProcessor->process($claim, $operation, $uriVariables, $context);
 
         return $this->autoMapper->map($claim, $data);
diff --git a/src/State/Project/SupportStateProcessor.php b/src/State/Project/SupportStateProcessor.php
index ec3002e..9276961 100644
--- a/src/State/Project/SupportStateProcessor.php
+++ b/src/State/Project/SupportStateProcessor.php
@@ -21,9 +21,13 @@ class SupportStateProcessor implements ProcessorInterface
         private EntityManagerInterface $entityManager,
     ) {}
 
+    /**
+     * @param SupportApiResource $data
+     *
+     * @return SupportApiResource
+     */
     public function process(mixed $data, Operation $operation, array $uriVariables = [], array $context = [])
     {
-        // Verify if the user is authenticated
         $user = $this->authService->getUser();
         if (!$user) {
             throw new AuthenticationException();
diff --git a/src/Validator/AvailableRewardUnits.php b/src/Validator/AvailableRewardUnits.php
new file mode 100644
index 0000000..1414e62
--- /dev/null
+++ b/src/Validator/AvailableRewardUnits.php
@@ -0,0 +1,11 @@
+<?php
+
+namespace App\Validator;
+
+use Symfony\Component\Validator\Constraint;
+
+#[\Attribute(\Attribute::TARGET_PROPERTY | \Attribute::TARGET_METHOD | \Attribute::IS_REPEATABLE)]
+final class AvailableRewardUnits extends Constraint
+{
+    public string $message = 'The ProjectReward "{{ id }}" has no units available.';
+}
diff --git a/src/Validator/AvailableRewardUnitsValidator.php b/src/Validator/AvailableRewardUnitsValidator.php
new file mode 100644
index 0000000..bf51d40
--- /dev/null
+++ b/src/Validator/AvailableRewardUnitsValidator.php
@@ -0,0 +1,29 @@
+<?php
+
+namespace App\Validator;
+
+use App\ApiResource\Project\RewardApiResource;
+use Symfony\Component\Validator\Constraint;
+use Symfony\Component\Validator\ConstraintValidator;
+
+final class AvailableRewardUnitsValidator extends ConstraintValidator
+{
+    /**
+     * @param RewardApiResource $value
+     */
+    public function validate(mixed $value, Constraint $constraint): void
+    {
+        if (!$value->hasUnits) {
+            return;
+        }
+
+        if ($value->hasUnits && $value->unitsAvailable > 0) {
+            return;
+        }
+
+        $this->context->buildViolation($constraint->message)
+            ->setParameter('{{ id }}', $value->id)
+            ->addViolation()
+        ;
+    }
+}
diff --git a/src/Validator/EnoughRewardCharge.php b/src/Validator/EnoughRewardCharge.php
new file mode 100644
index 0000000..f1bcb3c
--- /dev/null
+++ b/src/Validator/EnoughRewardCharge.php
@@ -0,0 +1,16 @@
+<?php
+
+namespace App\Validator;
+
+use Symfony\Component\Validator\Constraint;
+
+#[\Attribute(\Attribute::TARGET_CLASS)]
+final class EnoughRewardCharge extends Constraint
+{
+    public string $message = 'The charged money is not enough to claim the ProjectReward.';
+
+    public function getTargets(): string
+    {
+        return self::CLASS_CONSTRAINT;
+    }
+}
diff --git a/src/Validator/EnoughRewardChargeValidator.php b/src/Validator/EnoughRewardChargeValidator.php
new file mode 100644
index 0000000..bbf4017
--- /dev/null
+++ b/src/Validator/EnoughRewardChargeValidator.php
@@ -0,0 +1,33 @@
+<?php
+
+namespace App\Validator;
+
+use App\ApiResource\Project\RewardClaimApiResource;
+use App\Library\Economy\MoneyService;
+use Symfony\Component\Validator\Constraint;
+use Symfony\Component\Validator\ConstraintValidator;
+
+final class EnoughRewardChargeValidator extends ConstraintValidator
+{
+    public function __construct(
+        private MoneyService $money,
+    ) {}
+
+    /**
+     * @param RewardClaimApiResource $value
+     * @param EnoughRewardCharge     $constraint
+     */
+    public function validate(mixed $value, Constraint $constraint): void
+    {
+        $charge = $value->charge->money;
+        $reward = $value->reward->money;
+
+        if ($this->money->isMoreOrSame($charge, $reward)) {
+            return;
+        }
+
+        $this->context->buildViolation($constraint->message)
+            ->addViolation()
+        ;
+    }
+}