diff --git a/src/Adapter/ApplepayAdapter.php b/src/Adapter/ApplepayAdapter.php
index 820655cf9..3738586b0 100644
--- a/src/Adapter/ApplepayAdapter.php
+++ b/src/Adapter/ApplepayAdapter.php
@@ -37,7 +37,7 @@ public function validateApplePayMerchant(
         if ($this->request === null) {
             throw new ApplepayMerchantValidationException('No curl adapter initiated yet. Make sure to cal init() function before.');
         }
-        $payload = $applePaySession->jsonSerialize();
+        $payload = json_encode($applePaySession, JSON_UNESCAPED_SLASHES | JSON_PRESERVE_ZERO_FRACTION);
         $this->setOption(CURLOPT_URL, $merchantValidationURL);
         $this->setOption(CURLOPT_POSTFIELDS, $payload);
 
diff --git a/src/Resources/AbstractUnzerResource.php b/src/Resources/AbstractUnzerResource.php
index 59a3750d7..f3adf7bae 100644
--- a/src/Resources/AbstractUnzerResource.php
+++ b/src/Resources/AbstractUnzerResource.php
@@ -36,7 +36,7 @@
  * @link  https://docs.unzer.com/
  *
  */
-abstract class AbstractUnzerResource implements UnzerParentInterface
+abstract class AbstractUnzerResource implements UnzerParentInterface, \JsonSerializable
 {
     /** @var string $id */
     protected $id;
@@ -332,16 +332,11 @@ protected function fetchResource(AbstractUnzerResource $resource): void
     }
 
     /**
-     * Specify data which should be serialized to JSON
-     *
-     * @link http://php.net/manual/en/jsonserializable.jsonserialize.php
-     *
-     * @return false|string data which can be serialized by <b>json_encode</b>,
-     *                      which is a value of any type other than a resource.
+     * {@inheritDoc}
      */
-    public function jsonSerialize()
+    public function jsonSerialize(): mixed
     {
-        return json_encode($this->expose(), JSON_UNESCAPED_SLASHES | JSON_PRESERVE_ZERO_FRACTION);
+        return $this->expose();
     }
 
     /**
diff --git a/src/Resources/ExternalResources/ApplepaySession.php b/src/Resources/ExternalResources/ApplepaySession.php
index 2f3ebc7c4..29fa23e17 100644
--- a/src/Resources/ExternalResources/ApplepaySession.php
+++ b/src/Resources/ExternalResources/ApplepaySession.php
@@ -8,7 +8,7 @@
  *  @link  https://docs.unzer.com/
  *
  */
-class ApplepaySession
+class ApplepaySession implements \JsonSerializable
 {
     /**
      * This can be found in the Apple Developer Account
@@ -46,14 +46,11 @@ public function __construct(string $merchantIdentifier, string $displayName, str
     }
 
     /**
-     * Returns the json representation of this object's properties.
-     *
-     * @return false|string
+     * {@inheritDoc}
      */
-    public function jsonSerialize()
+    public function jsonSerialize(): mixed
     {
-        $properties = get_object_vars($this);
-        return json_encode($properties, JSON_UNESCAPED_SLASHES | JSON_PRESERVE_ZERO_FRACTION);
+        return get_object_vars($this);
     }
 
     /**
diff --git a/src/Services/HttpService.php b/src/Services/HttpService.php
index 68bcdc0c7..f341e86ac 100755
--- a/src/Services/HttpService.php
+++ b/src/Services/HttpService.php
@@ -128,7 +128,7 @@ public function sendRequest(ApiRequest $request): string
 
         // perform request
         $requestUrl = $this->buildRequestUrl($request);
-        $payload = $request->getResource()->jsonSerialize();
+        $payload = json_encode($request->getResource(), JSON_UNESCAPED_SLASHES | JSON_PRESERVE_ZERO_FRACTION);
         $headers = $this->composeHttpHeaders($unzerObj, $apiConfig::getAuthorizationMethod());
         $httpMethod = $request->getHttpMethod();
         $this->initRequest($requestUrl, $payload, $httpMethod, $headers);
diff --git a/src/Services/PaymentService.php b/src/Services/PaymentService.php
index e05dd4ccd..a8a11b2af 100755
--- a/src/Services/PaymentService.php
+++ b/src/Services/PaymentService.php
@@ -86,7 +86,7 @@ public function performAuthorization(
     ): Authorization {
         $payment = $this->createPayment($paymentType);
         $paymentType = $payment->getPaymentType();
-        $authorization->setSpecialParams($paymentType !== null ? $paymentType->getTransactionParams() : []);
+        $authorization->setSpecialParams($paymentType?->getTransactionParams() ?? []);
 
         $payment->setAuthorization($authorization)
             ->setCustomer($customer)
@@ -157,7 +157,7 @@ public function performCharge(Charge $charge, $paymentType, $customer = null, ?M
         $paymentType = $payment->getPaymentType();
 
         /** @var Charge $charge */
-        $charge->setSpecialParams($paymentType->getTransactionParams() ?? []);
+        $charge->setSpecialParams($paymentType?->getTransactionParams() ?? []);
         $payment->addCharge($charge)->setCustomer($customer)->setMetadata($metadata)->setBasket($basket);
 
         $this->getResourceService()->createResource($charge);
@@ -417,7 +417,7 @@ public function performSca(Sca $sca, $paymentType, $customer = null, ?Metadata $
         $paymentType = $payment->getPaymentType();
 
         /** @var Sca $sca */
-        $sca->setSpecialParams($paymentType->getTransactionParams() ?? []);
+        $sca->setSpecialParams($paymentType?->getTransactionParams() ?? []);
         $payment->setSca($sca)->setCustomer($customer)->setMetadata($metadata)->setBasket($basket);
 
         $this->getResourceService()->createResource($sca);
diff --git a/test/unit/Adapter/ApplepaySessionTest.php b/test/unit/Adapter/ApplepaySessionTest.php
index d2a225852..b9a1b9fe8 100644
--- a/test/unit/Adapter/ApplepaySessionTest.php
+++ b/test/unit/Adapter/ApplepaySessionTest.php
@@ -18,7 +18,7 @@ public function testJsonSerialize(): void
         $applepaySession = new ApplepaySession('merchantIdentifier', 'displayName', 'domainName');
         $expectedJson = '{"merchantIdentifier": "merchantIdentifier", "displayName": "displayName", "domainName": "domainName"}';
 
-        $jsonSerialize = $applepaySession->jsonSerialize();
+        $jsonSerialize = json_encode($applepaySession);
         $this->assertJsonStringEqualsJsonString($expectedJson, $jsonSerialize);
     }
 }
diff --git a/test/unit/DummyResource.php b/test/unit/DummyResource.php
index 2a7f34c7a..717308e88 100755
--- a/test/unit/DummyResource.php
+++ b/test/unit/DummyResource.php
@@ -43,9 +43,9 @@ public function setTestFloat(float $testFloat): DummyResource
     //</editor-fold>
 
     //<editor-fold desc="Overridable methods">
-    public function jsonSerialize()
+    public function jsonSerialize(): mixed
     {
-        return '{"dummyResource": "JsonSerialized"}';
+        return ['dummyResource' => 'JsonSerialized'];
     }
 
     public function getUri(bool $appendId = true, string $httpMethod = HttpAdapterInterface::REQUEST_GET): string
diff --git a/test/unit/Resources/AbstractUnzerResourceTest.php b/test/unit/Resources/AbstractUnzerResourceTest.php
index 5e6b0194c..e485895b0 100644
--- a/test/unit/Resources/AbstractUnzerResourceTest.php
+++ b/test/unit/Resources/AbstractUnzerResourceTest.php
@@ -239,8 +239,8 @@ public function updateValuesShouldUpdateChildObjects(): void
             ->setCommercialSector(CompanyCommercialSectorItems::AIR_TRANSPORT);
 
         $testResponse                 = new stdClass();
-        $testResponse->billingAddress = json_decode($address->jsonSerialize(), false);
-        $testResponse->companyInfo    = json_decode($info->jsonSerialize(), false);
+        $testResponse->billingAddress = json_decode(json_encode($address), false);
+        $testResponse->companyInfo    = json_decode(json_encode($info), false);
 
         $customer = new Customer();
         $customer->handleResponse($testResponse);
@@ -319,7 +319,7 @@ public function jsonSerializeShouldTranslateResourceIntoJson(): void
             '"firstname":"Peter","lastname":"Universum","mobile":"+49172123456","param1":"value1","param2":"value2",' .
             '"phone":"+4962216471100","salutation":"mr","shippingAddress":{"city":"Frankfurt am Main","country":"DE",' .
             '"name":"Peter Universum","state":"DE-BO","street":"Hugo-Junkers-Str. 5","zip":"60386"}}';
-        $this->assertEquals($expectedJson, $customer->jsonSerialize());
+        $this->assertJsonStringEqualsJsonString($expectedJson, json_encode($customer));
     }
 
     /**
@@ -423,8 +423,8 @@ public function parentPrivatePropertiesShouldNotCauseAnException(): void
         $metadata->setParentResource(new Unzer('s-priv-123'));
         $metadata->setSpecialParams(['something' => 'special']);
 
-        $result = $metadata->jsonSerialize();
-        $this->assertEquals('{"something":"special"}', $result);
+        $result = json_encode($metadata);
+        $this->assertJsonStringEqualsJsonString('{"something":"special"}', $result);
     }
 
     //<editor-fold desc="Data Providers">
diff --git a/test/unit/Resources/PaymentTypes/ApplePayTest.php b/test/unit/Resources/PaymentTypes/ApplePayTest.php
index 7d33e684e..f4e58fb15 100644
--- a/test/unit/Resources/PaymentTypes/ApplePayTest.php
+++ b/test/unit/Resources/PaymentTypes/ApplePayTest.php
@@ -47,7 +47,7 @@ public function jsonSerializationExposesOnlyRequestParameter(): void
         $expectedJson = '{ "data": "data", "header": { "ephemeralPublicKey": "ephemeralPublicKey", "publicKeyHash": ' .
             '"publicKeyHash", "transactionId": "transactionId" }, "signature": "sig", "version": "EC_v1" }';
 
-        $this->assertJsonStringEqualsJsonString($expectedJson, $applepay->jsonSerialize());
+        $this->assertJsonStringEqualsJsonString($expectedJson, json_encode($applepay));
     }
 
     /**
diff --git a/test/unit/Resources/PaymentTypes/ClickToPayTest.php b/test/unit/Resources/PaymentTypes/ClickToPayTest.php
index 943726a29..265a7b185 100644
--- a/test/unit/Resources/PaymentTypes/ClickToPayTest.php
+++ b/test/unit/Resources/PaymentTypes/ClickToPayTest.php
@@ -44,7 +44,7 @@ public function jsonSerialization(): void
         );
 
         $expectedJson = JsonProvider::getJsonFromFile('clicktopay/createRequest.json');
-        $this->assertJsonStringEqualsJsonString($expectedJson, $clickToPayObject->jsonSerialize());
+        $this->assertJsonStringEqualsJsonString($expectedJson, json_encode($clickToPayObject));
     }
 
     /**
diff --git a/test/unit/Resources/PaymentTypes/GooglePayTest.php b/test/unit/Resources/PaymentTypes/GooglePayTest.php
index 80559db3a..304a4a4cf 100644
--- a/test/unit/Resources/PaymentTypes/GooglePayTest.php
+++ b/test/unit/Resources/PaymentTypes/GooglePayTest.php
@@ -46,7 +46,7 @@ public function jsonSerializationExposesOnlyRequestParameter(): void
         $googlepay = $this->getTestGooglepay();
 
         $expectedJson = JsonProvider::getJsonFromFile('googlePay/createRequest.json');
-        $this->assertJsonStringEqualsJsonString($expectedJson, $googlepay->jsonSerialize());
+        $this->assertJsonStringEqualsJsonString($expectedJson, json_encode($googlepay));
     }
 
     /**
diff --git a/test/unit/Resources/PaymentTypes/OpenBankingTest.php b/test/unit/Resources/PaymentTypes/OpenBankingTest.php
index 765d40d8e..5addf7d24 100644
--- a/test/unit/Resources/PaymentTypes/OpenBankingTest.php
+++ b/test/unit/Resources/PaymentTypes/OpenBankingTest.php
@@ -33,7 +33,7 @@ public function jsonSerialization(): void
         $openBankingObject = new OpenbankingPis("DE",);
 
         $expectedJson = JsonProvider::getJsonFromFile('openBanking/createRequest.json');
-        $this->assertJsonStringEqualsJsonString($expectedJson, $openBankingObject->jsonSerialize());
+        $this->assertJsonStringEqualsJsonString($expectedJson, json_encode($openBankingObject));
     }
 
     /**
diff --git a/test/unit/Services/HttpServiceTest.php b/test/unit/Services/HttpServiceTest.php
index 816b43fe8..f2e60cd91 100755
--- a/test/unit/Services/HttpServiceTest.php
+++ b/test/unit/Services/HttpServiceTest.php
@@ -97,7 +97,7 @@ static function ($url) {
                     return str_replace(['dev-api', 'stg-api'], 'sbx-api', $url) === 'https://sbx-api.unzer.com/v1/my/uri/123';
                 }
             ),
-            '{"dummyResource": "JsonSerialized"}',
+            '{"dummyResource":"JsonSerialized"}',
             'GET'
         );
         /** @noinspection PhpParamsInspection */
@@ -223,7 +223,7 @@ static function ($string) {
                 }
             )
             ],
-            ['(' . (getmypid()) . ') Request: {"dummyResource": "JsonSerialized"}'],
+            ['(' . (getmypid()) . ') Request: {"dummyResource":"JsonSerialized"}'],
             ['(' . (getmypid()) . ') Response: (201) {"response":"myResponseString"}']
         );
 
diff --git a/test/unit/Services/PaymentServiceTest.php b/test/unit/Services/PaymentServiceTest.php
index f73cb6c8f..ea3441cc9 100755
--- a/test/unit/Services/PaymentServiceTest.php
+++ b/test/unit/Services/PaymentServiceTest.php
@@ -31,6 +31,7 @@
 use UnzerSDK\Resources\TransactionTypes\Cancellation;
 use UnzerSDK\Resources\TransactionTypes\Charge;
 use UnzerSDK\Resources\TransactionTypes\Payout;
+use UnzerSDK\Resources\TransactionTypes\Sca;
 use UnzerSDK\Resources\TransactionTypes\Shipment;
 use UnzerSDK\Services\CancelService;
 use UnzerSDK\Services\PaymentService;
@@ -283,6 +284,42 @@ public function chargePaymentShouldSetArgumentsInNewChargeObject(): void
         $this->assertEquals([$returnedCharge], $payment->getCharges());
     }
 
+    /**
+     * Verify performCharge does not throw a fatal error when the payment type resolves to null.
+     *
+     * @test
+     */
+    public function performChargeWithNullPaymentTypeShouldNotThrowFatalError(): void
+    {
+        $resourceSrvMock = $this->getMockBuilder(ResourceService::class)->disableOriginalConstructor()->setMethods(['createResource'])->getMock();
+        $paymentSrv = (new Unzer('s-priv-123'))->setResourceService($resourceSrvMock)->getPaymentService();
+
+        try {
+            $paymentSrv->performCharge(new Charge(), null);
+            $this->assertTrue(true);
+        } catch (\Throwable $e) {
+            $this->fail('performCharge threw an unexpected error: ' . $e->getMessage());
+        }
+    }
+
+    /**
+     * Verify performSca does not throw a fatal error when the payment type resolves to null.
+     *
+     * @test
+     */
+    public function performScaWithNullPaymentTypeShouldNotThrowFatalError(): void
+    {
+        $resourceSrvMock = $this->getMockBuilder(ResourceService::class)->disableOriginalConstructor()->setMethods(['createResource'])->getMock();
+        $paymentSrv = (new Unzer('s-priv-123'))->setResourceService($resourceSrvMock)->getPaymentService();
+
+        try {
+            $paymentSrv->performSca(new Sca(), null);
+            $this->assertTrue(true);
+        } catch (\Throwable $e) {
+            $this->fail('performSca threw an unexpected error: ' . $e->getMessage());
+        }
+    }
+
     //</editor-fold>
 
     //<editor-fold desc="Cancel">
diff --git a/test/unit/Traits/HasRecurrenceTypeTest.php b/test/unit/Traits/HasRecurrenceTypeTest.php
index f2044f275..36a0539d9 100644
--- a/test/unit/Traits/HasRecurrenceTypeTest.php
+++ b/test/unit/Traits/HasRecurrenceTypeTest.php
@@ -76,7 +76,7 @@ public function recurrenceTypeShouldBeExposedProperly(): void
         $this->assertEquals('oneclick', $exposedTransaction['additionalTransactionData']->card['recurrenceType']);
         $this->assertStringContainsString(
             '"additionalTransactionData":{"card":{"recurrenceType":"oneclick"}}',
-            $charge->jsonSerialize()
+            json_encode($charge)
         );
     }
 
@@ -108,7 +108,7 @@ public function responseShouldBeHandledProperlyWithRecurrenceType(): void
         $this->assertEquals('oneclick', $charge->getRecurrenceType());
         $this->assertStringContainsString(
             '"additionalTransactionData":{"card":{"recurrenceType":"oneclick"}}',
-            $charge->jsonSerialize()
+            json_encode($charge)
         );
     }