diff --git a/src/PhpPact/Consumer/Driver/Body/InteractionBodyDriver.php b/src/PhpPact/Consumer/Driver/Body/InteractionBodyDriver.php
index 77bad1ec..f04cc5f2 100644
--- a/src/PhpPact/Consumer/Driver/Body/InteractionBodyDriver.php
+++ b/src/PhpPact/Consumer/Driver/Body/InteractionBodyDriver.php
@@ -2,8 +2,6 @@
 
 namespace PhpPact\Consumer\Driver\Body;
 
-use FFI;
-use FFI\CData;
 use PhpPact\Consumer\Driver\Enum\InteractionPart;
 use PhpPact\Consumer\Driver\Exception\InteractionBodyNotAddedException;
 use PhpPact\Consumer\Driver\Exception\PartNotAddedException;
@@ -23,8 +21,8 @@ public function registerBody(Interaction $interaction, InteractionPart $interact
     {
         $body = $interaction->getBody($interactionPart);
         $partId = match ($interactionPart) {
-            InteractionPart::REQUEST => $this->client->get('InteractionPart_Request'),
-            InteractionPart::RESPONSE => $this->client->get('InteractionPart_Response'),
+            InteractionPart::REQUEST => $this->client->getInteractionPartRequest(),
+            InteractionPart::RESPONSE => $this->client->getInteractionPartResponse(),
         };
         switch (true) {
             case $body instanceof Binary:
@@ -38,9 +36,9 @@ public function registerBody(Interaction $interaction, InteractionPart $interact
 
             case $body instanceof Multipart:
                 foreach ($body->getParts() as $part) {
-                    $result = $this->client->call('pactffi_with_multipart_file_v2', $interaction->getHandle(), $partId, $part->getContentType(), $part->getPath(), $part->getName(), $body->getBoundary());
-                    if ($result->failed instanceof CData) {
-                        throw new PartNotAddedException(sprintf("Can not add part '%s': %s", $part->getName(), FFI::string($result->failed)));
+                    $result = $this->client->withMultipartFileV2($interaction->getHandle(), $partId, $part->getContentType(), $part->getPath(), $part->getName(), $body->getBoundary());
+                    if (!$result->success) {
+                        throw new PartNotAddedException(sprintf("Can not add part '%s': %s", $part->getName(), $result->message));
                     }
                 }
                 $success = true;
diff --git a/src/PhpPact/FFI/Client.php b/src/PhpPact/FFI/Client.php
index 38b54a2b..d61cb01a 100644
--- a/src/PhpPact/FFI/Client.php
+++ b/src/PhpPact/FFI/Client.php
@@ -3,7 +3,11 @@
 namespace PhpPact\FFI;
 
 use FFI;
+use FFI\CData;
 use PhpPact\FFI\Exception\HeaderNotReadException;
+use PhpPact\FFI\Exception\InvalidEnumException;
+use PhpPact\FFI\Exception\InvalidResultException;
+use PhpPact\FFI\Model\Result;
 use PhpPact\Standalone\Installer\Model\Scripts;
 
 class Client implements ClientInterface
@@ -12,13 +16,49 @@ class Client implements ClientInterface
 
     public function __construct()
     {
-        $code = \file_get_contents(Scripts::getHeader());
+        $headerFile = Scripts::getHeader();
+        $code = \file_get_contents($headerFile);
         if (!is_string($code)) {
-            throw new HeaderNotReadException();
+            throw new HeaderNotReadException(sprintf('Can not read header file "%s"', $headerFile));
         }
         $this->ffi = FFI::cdef($code, Scripts::getLibrary());
     }
 
+    public function withMultipartFileV2(int $interaction, int $part, string $contentType, string $path, string $name, string $boundary): Result
+    {
+        $method = 'pactffi_with_multipart_file_v2';
+        $result = $this->call($method, $interaction, $part, $contentType, $path, $name, $boundary);
+        if (!$result instanceof CData) {
+            throw new InvalidResultException(sprintf('Invalid result of "%s". Expected "%s", but got "%s"', $method, CData::class, get_debug_type($result)));
+        }
+        if ($result->tag === $this->getEnum('StringResult_Ok')) { // @phpstan-ignore-line
+            return new Result(true, $result->ok instanceof CData ? FFI::string($result->ok) : ''); // @phpstan-ignore-line
+        }
+        if ($result->tag === $this->getEnum('StringResult_Failed')) { // @phpstan-ignore-line
+            return new Result(false, $result->failed instanceof CData ? FFI::string($result->failed) : ''); // @phpstan-ignore-line
+        }
+        throw new InvalidResultException(sprintf('Invalid result of "%s". Neither ok or failed', $method));
+    }
+
+    public function getInteractionPartRequest(): int
+    {
+        return $this->getEnum('InteractionPart_Request');
+    }
+
+    public function getInteractionPartResponse(): int
+    {
+        return $this->getEnum('InteractionPart_Response');
+    }
+
+    private function getEnum(string $name): int
+    {
+        $value = $this->get($name);
+        if (!is_int($value)) {
+            throw new InvalidEnumException(sprintf('Invalid enum "%s". Expected "int", but got "%s"', $name, get_debug_type($value)));
+        }
+        return $value;
+    }
+
     public function call(string $name, ...$arguments): mixed
     {
         return $this->ffi->{$name}(...$arguments);
diff --git a/src/PhpPact/FFI/ClientInterface.php b/src/PhpPact/FFI/ClientInterface.php
index c0e767ff..11927df6 100644
--- a/src/PhpPact/FFI/ClientInterface.php
+++ b/src/PhpPact/FFI/ClientInterface.php
@@ -2,8 +2,16 @@
 
 namespace PhpPact\FFI;
 
+use PhpPact\FFI\Model\Result;
+
 interface ClientInterface
 {
+    public function withMultipartFileV2(int $interaction, int $part, string $contentType, string $path, string $name, string $boundary): Result;
+
+    public function getInteractionPartRequest(): int;
+
+    public function getInteractionPartResponse(): int;
+
     /**
      * @param array<int, mixed> $arguments
      */
diff --git a/src/PhpPact/FFI/Exception/InvalidEnumException.php b/src/PhpPact/FFI/Exception/InvalidEnumException.php
new file mode 100644
index 00000000..e08e6786
--- /dev/null
+++ b/src/PhpPact/FFI/Exception/InvalidEnumException.php
@@ -0,0 +1,7 @@
+<?php
+
+namespace PhpPact\FFI\Exception;
+
+class InvalidEnumException extends FFIException
+{
+}
diff --git a/src/PhpPact/FFI/Exception/InvalidResultException.php b/src/PhpPact/FFI/Exception/InvalidResultException.php
new file mode 100644
index 00000000..ecf8afb3
--- /dev/null
+++ b/src/PhpPact/FFI/Exception/InvalidResultException.php
@@ -0,0 +1,7 @@
+<?php
+
+namespace PhpPact\FFI\Exception;
+
+class InvalidResultException extends FFIException
+{
+}
diff --git a/src/PhpPact/FFI/Model/Result.php b/src/PhpPact/FFI/Model/Result.php
new file mode 100644
index 00000000..96d5280d
--- /dev/null
+++ b/src/PhpPact/FFI/Model/Result.php
@@ -0,0 +1,12 @@
+<?php
+
+namespace PhpPact\FFI\Model;
+
+class Result
+{
+    public function __construct(
+        public readonly bool $success,
+        public readonly string $message
+    ) {
+    }
+}
diff --git a/tests/PhpPact/Consumer/Driver/Body/InteractionBodyDriverTest.php b/tests/PhpPact/Consumer/Driver/Body/InteractionBodyDriverTest.php
index e10dc109..2c921115 100644
--- a/tests/PhpPact/Consumer/Driver/Body/InteractionBodyDriverTest.php
+++ b/tests/PhpPact/Consumer/Driver/Body/InteractionBodyDriverTest.php
@@ -2,8 +2,6 @@
 
 namespace PhpPactTest\Consumer\Driver\Body;
 
-use FFI;
-use FFI\CData;
 use PhpPact\Consumer\Driver\Body\InteractionBodyDriver;
 use PhpPact\Consumer\Driver\Body\InteractionBodyDriverInterface;
 use PhpPact\Consumer\Driver\Enum\InteractionPart;
@@ -17,6 +15,7 @@
 use PhpPact\Consumer\Model\Interaction;
 use PhpPact\Consumer\Model\ProviderResponse;
 use PhpPact\FFI\ClientInterface;
+use PhpPact\FFI\Model\Result;
 use PHPUnit\Framework\Attributes\TestWith;
 use PHPUnit\Framework\MockObject\MockObject;
 use PHPUnit\Framework\TestCase;
@@ -37,19 +36,11 @@ class InteractionBodyDriverTest extends TestCase
      */
     private array $parts;
     private string $boundary = 'abcde12345';
-    private CData $failed;
     private string $message = 'error';
 
     public function setUp(): void
     {
         $this->client = $this->createMock(ClientInterface::class);
-        $this->client
-            ->expects($this->once())
-            ->method('get')
-            ->willReturnMap([
-                ['InteractionPart_Request', $this->requestPartId],
-                ['InteractionPart_Response', $this->responsePartId],
-            ]);
         $this->driver = new InteractionBodyDriver($this->client);
         $this->interaction = new Interaction();
         $this->interaction->setHandle($this->interactionHandle);
@@ -63,14 +54,13 @@ public function setUp(): void
             new Part('/path/to//image.png', 'profileImage', 'image/png'),
         ];
         $this->multipart = new Multipart($this->parts, $this->boundary);
-        $this->failed = FFI::new('char[5]');
-        FFI::memcpy($this->failed, $this->message, 5);
     }
 
     #[TestWith([true])]
     #[TestWith([false])]
     public function testRequestBinaryBody(bool $success): void
     {
+        $this->expectsGetEnumMethods(InteractionPart::REQUEST);
         $data = $this->binary->getData();
         $this->interaction->getRequest()->setBody($this->binary);
         $this->client
@@ -88,6 +78,7 @@ public function testRequestBinaryBody(bool $success): void
     #[TestWith([false])]
     public function testResponseBinaryBody(bool $success): void
     {
+        $this->expectsGetEnumMethods(InteractionPart::RESPONSE);
         $data = $this->binary->getData();
         $this->interaction->getResponse()->setBody($this->binary);
         $this->client
@@ -105,6 +96,7 @@ public function testResponseBinaryBody(bool $success): void
     #[TestWith([false])]
     public function testRequestTextBody(bool $success): void
     {
+        $this->expectsGetEnumMethods(InteractionPart::REQUEST);
         $this->interaction->getRequest()->setBody($this->text);
         $this->client
             ->expects($this->once())
@@ -121,6 +113,7 @@ public function testRequestTextBody(bool $success): void
     #[TestWith([false])]
     public function testResponseTextBody(bool $success): void
     {
+        $this->expectsGetEnumMethods(InteractionPart::RESPONSE);
         $this->interaction->getResponse()->setBody($this->text);
         $this->client
             ->expects($this->once())
@@ -137,25 +130,26 @@ public function testResponseTextBody(bool $success): void
     #[TestWith([false])]
     public function testRequestMultipartBody(bool $success): void
     {
+        $this->expectsGetEnumMethods(InteractionPart::REQUEST);
         $this->interaction->getRequest()->setBody($this->multipart);
         $matcher = $this->exactly(count($this->parts));
         $calls = [
             [
-                'args' => ['pactffi_with_multipart_file_v2', $this->interactionHandle, $this->requestPartId, $this->parts[0]->getContentType(), $this->parts[0]->getPath(), $this->parts[0]->getName(), $this->boundary],
-                'return' => (object) ['failed' => null],
+                'args' => [$this->interactionHandle, $this->requestPartId, $this->parts[0]->getContentType(), $this->parts[0]->getPath(), $this->parts[0]->getName(), $this->boundary],
+                'return' => new Result(true, ''),
             ],
             [
-                'args' => ['pactffi_with_multipart_file_v2', $this->interactionHandle, $this->requestPartId, $this->parts[1]->getContentType(), $this->parts[1]->getPath(), $this->parts[1]->getName(), $this->boundary],
-                'return' => (object) ['failed' => null],
+                'args' => [$this->interactionHandle, $this->requestPartId, $this->parts[1]->getContentType(), $this->parts[1]->getPath(), $this->parts[1]->getName(), $this->boundary],
+                'return' => new Result(true, ''),
             ],
             [
-                'args' => ['pactffi_with_multipart_file_v2', $this->interactionHandle, $this->requestPartId, $this->parts[2]->getContentType(), $this->parts[2]->getPath(), $this->parts[2]->getName(), $this->boundary],
-                'return' => (object) (['failed' => $success ? null : $this->failed]),
+                'args' => [$this->interactionHandle, $this->requestPartId, $this->parts[2]->getContentType(), $this->parts[2]->getPath(), $this->parts[2]->getName(), $this->boundary],
+                'return' => new Result($success, $success ? '' : $this->message),
             ]
         ];
         $this->client
             ->expects($matcher)
-            ->method('call')
+            ->method('withMultipartFileV2')
             ->willReturnCallback(
                 function (...$args) use ($calls, $matcher) {
                     $index = $matcher->numberOfInvocations() - 1;
@@ -176,25 +170,26 @@ function (...$args) use ($calls, $matcher) {
     #[TestWith([false])]
     public function testResponseMultipartBody(bool $success): void
     {
+        $this->expectsGetEnumMethods(InteractionPart::RESPONSE);
         $this->interaction->getResponse()->setBody($this->multipart);
         $matcher = $this->exactly(count($this->parts));
         $calls = [
             [
-                'args' => ['pactffi_with_multipart_file_v2', $this->interactionHandle, $this->responsePartId, $this->parts[0]->getContentType(), $this->parts[0]->getPath(), $this->parts[0]->getName(), $this->boundary],
-                'return' => (object) ['failed' => null],
+                'args' => [$this->interactionHandle, $this->responsePartId, $this->parts[0]->getContentType(), $this->parts[0]->getPath(), $this->parts[0]->getName(), $this->boundary],
+                'return' => new Result(true, ''),
             ],
             [
-                'args' => ['pactffi_with_multipart_file_v2', $this->interactionHandle, $this->responsePartId, $this->parts[1]->getContentType(), $this->parts[1]->getPath(), $this->parts[1]->getName(), $this->boundary],
-                'return' => (object) ['failed' => null],
+                'args' => [$this->interactionHandle, $this->responsePartId, $this->parts[1]->getContentType(), $this->parts[1]->getPath(), $this->parts[1]->getName(), $this->boundary],
+                'return' => new Result(true, ''),
             ],
             [
-                'args' => ['pactffi_with_multipart_file_v2', $this->interactionHandle, $this->responsePartId, $this->parts[2]->getContentType(), $this->parts[2]->getPath(), $this->parts[2]->getName(), $this->boundary],
-                'return' => (object) (['failed' => $success ? null : $this->failed]),
+                'args' => [$this->interactionHandle, $this->responsePartId, $this->parts[2]->getContentType(), $this->parts[2]->getPath(), $this->parts[2]->getName(), $this->boundary],
+                'return' => new Result($success, $success ? '' : $this->message),
             ]
         ];
         $this->client
             ->expects($matcher)
-            ->method('call')
+            ->method('withMultipartFileV2')
             ->willReturnCallback(
                 function (...$args) use ($calls, $matcher) {
                     $index = $matcher->numberOfInvocations() - 1;
@@ -215,9 +210,30 @@ function (...$args) use ($calls, $matcher) {
     #[TestWith([InteractionPart::RESPONSE])]
     public function testEmptyBody(InteractionPart $part): void
     {
+        $this->expectsGetEnumMethods($part);
         $this->client
             ->expects($this->never())
             ->method('call');
+        $this->client
+            ->expects($this->never())
+            ->method('withMultipartFileV2');
         $this->driver->registerBody($this->interaction, $part);
     }
+
+    private function expectsGetEnumMethods(InteractionPart $part): void
+    {
+        if ($part === InteractionPart::REQUEST) {
+            $this->client
+                ->expects($this->once())
+                ->method('getInteractionPartRequest')
+                ->willReturn($this->requestPartId);
+            $this->client->expects($this->never())->method('getInteractionPartResponse');
+        } else {
+            $this->client->expects($this->never())->method('getInteractionPartRequest');
+            $this->client
+                ->expects($this->once())
+                ->method('getInteractionPartResponse')
+                ->willReturn($this->responsePartId);
+        }
+    }
 }
diff --git a/tests/PhpPact/FFI/ClientTest.php b/tests/PhpPact/FFI/ClientTest.php
index 9aca443c..7baec03b 100644
--- a/tests/PhpPact/FFI/ClientTest.php
+++ b/tests/PhpPact/FFI/ClientTest.php
@@ -2,7 +2,6 @@
 
 namespace PhpPactTest\FFI;
 
-use FFI;
 use PhpPact\FFI\Client;
 use PhpPact\FFI\ClientInterface;
 use PHPUnit\Framework\Attributes\TestWith;
@@ -17,6 +16,23 @@ public function setUp(): void
         $this->client = new Client();
     }
 
+    public function testWithMultipartFileV2(): void
+    {
+        $result = $this->client->withMultipartFileV2(1, 2, 'text/plain', './path/to/file.txt', 'text', 'abc123');
+        $this->assertFalse($result->success);
+        $this->assertSame('with_multipart_file: Interaction handle is invalid', $result->message);
+    }
+
+    public function testGetInteractionPartRequest(): void
+    {
+        $this->assertSame(0, $this->client->getInteractionPartRequest());
+    }
+
+    public function testGetInteractionPartResponse(): void
+    {
+        $this->assertSame(1, $this->client->getInteractionPartResponse());
+    }
+
     public function testGet(): void
     {
         $this->assertSame(5, $this->client->get('LevelFilter_Trace'));