diff --git a/src/Coupon/CouponResource.php b/src/Coupon/CouponResource.php
index 5a721b3..a38327c 100644
--- a/src/Coupon/CouponResource.php
+++ b/src/Coupon/CouponResource.php
@@ -28,7 +28,7 @@ public function create(CreateCouponRequest $request): CouponResponse
     {
         try {
             $response = $this->client->post(sprintf('%s/create', self::BASE_PATH), [
-                'json' => $request->jsonSerialize(),
+                'json' => $request->toArray(),
             ]);
 
             $responsePayload = json_decode(
diff --git a/src/Coupon/Http/Request/CreateCouponRequest.php b/src/Coupon/Http/Request/CreateCouponRequest.php
index 1944872..f765943 100644
--- a/src/Coupon/Http/Request/CreateCouponRequest.php
+++ b/src/Coupon/Http/Request/CreateCouponRequest.php
@@ -6,9 +6,8 @@
 
 use Basement\AbacatePay\Coupon\Enums\CouponDiscountKindEnum;
 use Basement\AbacatePay\Coupon\Http\Builder\CreateCouponRequestBuilder;
-use JsonSerializable;
 
-final readonly class CreateCouponRequest implements JsonSerializable
+final readonly class CreateCouponRequest
 {
     public function __construct(
         public string $code,
@@ -36,7 +35,7 @@ public static function builder(): CreateCouponRequestBuilder
         return new CreateCouponRequestBuilder;
     }
 
-    public function jsonSerialize(): array
+    public function toArray(): array
     {
         return [
             'code' => $this->code,
diff --git a/src/Pix/Entities/PixQrCodeEntity.php b/src/Pix/Entities/PixQrCodeEntity.php
index e94cae6..4b84185 100644
--- a/src/Pix/Entities/PixQrCodeEntity.php
+++ b/src/Pix/Entities/PixQrCodeEntity.php
@@ -4,15 +4,11 @@
 
 namespace Basement\AbacatePay\Pix\Entities;
 
-use Basement\AbacatePay\Billing\Enum\BillingMethodEnum;
 use Basement\AbacatePay\Billing\Enum\BillingStatusEnum;
 use JsonSerializable;
 
 final readonly class PixQrCodeEntity implements JsonSerializable
 {
-    /**
-     * @param  BillingMethodEnum[]  $methods
-     */
     public function __construct(
         public string $id,
         public int $amount,
diff --git a/src/Pix/Http/Builder/CreatePixQrCodeRequestBuilder.php b/src/Pix/Http/Builder/CreatePixQrCodeRequestBuilder.php
index 8200060..d247fc6 100644
--- a/src/Pix/Http/Builder/CreatePixQrCodeRequestBuilder.php
+++ b/src/Pix/Http/Builder/CreatePixQrCodeRequestBuilder.php
@@ -28,28 +28,28 @@ public function amount(int $amount): self
         return $this;
     }
 
-    public function expiresIn(int $seconds): self
+    public function expiresIn(?int $seconds): self
     {
         $this->expiresIn = $seconds;
 
         return $this;
     }
 
-    public function description(string $description): self
+    public function description(?string $description): self
     {
         $this->description = $description;
 
         return $this;
     }
 
-    public function customer(PixCustomerRequest $customer): self
+    public function customer(?PixCustomerRequest $customer): self
     {
         $this->customer = $customer;
 
         return $this;
     }
 
-    public function metadata(PixMetadataRequest $metadata): self
+    public function metadata(?PixMetadataRequest $metadata): self
     {
         $this->metadata = $metadata;
 
@@ -61,36 +61,14 @@ public function metadata(PixMetadataRequest $metadata): self
      */
     public function build(): CreatePixQrCodeRequest
     {
-        $errors = [];
-
         if ($this->amount === null) {
-            $errors[] = 'amount';
-        }
-
-        if ($this->expiresIn === null) {
-            $errors[] = 'expiresIn';
-        }
-
-        if ($this->description === null) {
-            $errors[] = 'description';
-        }
-
-        if (! $this->customer instanceof PixCustomerRequest) {
-            $errors[] = 'customer';
-        }
-
-        if (! $this->metadata instanceof PixMetadataRequest) {
-            $errors[] = 'metadata';
-        }
-
-        if ($errors !== []) {
-            throw AbacatePayException::missingRequiredFields($errors);
+            throw AbacatePayException::missingRequiredFields(['amount']);
         }
 
         return new CreatePixQrCodeRequest(
             amount: $this->amount,
-            expiresIn: $this->expiresIn,
-            description: $this->description,
+            expiresIn: $this->expiresIn ?? null,
+            description: $this->description ?? null,
             customer: $this->customer,
             metadata: $this->metadata,
         );
diff --git a/src/Pix/Http/Request/CreatePixQrCodeRequest.php b/src/Pix/Http/Request/CreatePixQrCodeRequest.php
index 96b3754..15b5f13 100644
--- a/src/Pix/Http/Request/CreatePixQrCodeRequest.php
+++ b/src/Pix/Http/Request/CreatePixQrCodeRequest.php
@@ -5,16 +5,15 @@
 namespace Basement\AbacatePay\Pix\Http\Request;
 
 use Basement\AbacatePay\Pix\Http\Builder\CreatePixQrCodeRequestBuilder;
-use JsonSerializable;
 
-final readonly class CreatePixQrCodeRequest implements JsonSerializable
+final readonly class CreatePixQrCodeRequest
 {
     public function __construct(
         public int $amount,
-        public int $expiresIn,
-        public string $description,
-        public PixCustomerRequest $customer,
-        public PixMetadataRequest $metadata,
+        public ?int $expiresIn,
+        public ?string $description,
+        public ?PixCustomerRequest $customer,
+        public ?PixMetadataRequest $metadata,
     ) {}
 
     public static function builder(): CreatePixQrCodeRequestBuilder
@@ -26,21 +25,33 @@ public static function make(array $data): self
     {
         return new self(
             amount: $data['amount'],
-            expiresIn: $data['expiresIn'],
-            description: $data['description'],
-            customer: $data['customer'],
-            metadata: $data['metadata'],
+            expiresIn: $data['expiresIn'] ?? null,
+            description: $data['description'] ?? null,
+            customer: $data['customer'] ?? null,
+            metadata: $data['metadata'] ?? null,
         );
     }
 
-    public function jsonSerialize(): array
+    public function toArray(): array
     {
-        return [
-            'amount' => $this->amount,
-            'expiresIn' => $this->expiresIn,
-            'description' => $this->description,
-            'customer' => $this->customer->toArray(),
-            'metadata' => $this->metadata->toArray(),
-        ];
+        $data = ['amount' => $this->amount];
+
+        if ($this->expiresIn !== null) {
+            $data['expiresIn'] = $this->expiresIn;
+        }
+
+        if ($this->description !== null) {
+            $data['description'] = $this->description;
+        }
+
+        if ($this->customer instanceof PixCustomerRequest) {
+            $data['customer'] = $this->customer->toArray();
+        }
+
+        if ($this->metadata instanceof PixMetadataRequest) {
+            $data['metadata'] = $this->metadata->toArray();
+        }
+
+        return $data;
     }
 }
diff --git a/src/Pix/PixResource.php b/src/Pix/PixResource.php
index 25f2783..201cb3b 100644
--- a/src/Pix/PixResource.php
+++ b/src/Pix/PixResource.php
@@ -29,7 +29,7 @@ public function createQrCode(CreatePixQrCodeRequest $request): CreatePixQrCodeRe
     {
         try {
             $response = $this->client->post(sprintf('%s/create', self::BASE_PATH), [
-                'json' => $request->jsonSerialize(),
+                'json' => $request->toArray(),
             ]);
 
             $responsePayload = json_decode(
diff --git a/tests/Feature/Billing/BillingFeatureTest.php b/tests/Feature/Billing/BillingFeatureTest.php
index 7cb08d2..bad8924 100644
--- a/tests/Feature/Billing/BillingFeatureTest.php
+++ b/tests/Feature/Billing/BillingFeatureTest.php
@@ -111,10 +111,10 @@
         products: [],
         return_url: 'https://example.com/return',
         completion_url: 'https://example.com/complete',
-        customerId: null,
-        customer: null,
         allow_coupons: false,
         coupons: [],
+        customerId: null,
+        customer: null,
         externalId: null
     );
 
@@ -140,10 +140,10 @@
         products: [],
         return_url: 'https://example.com/return',
         completion_url: 'https://example.com/complete',
-        customerId: null,
-        customer: null,
         allow_coupons: false,
         coupons: [],
+        customerId: null,
+        customer: null,
         externalId: null
     );
 
diff --git a/tests/Feature/Pix/PixResourceTest.php b/tests/Feature/Pix/PixResourceTest.php
index 07481c3..f3b5db0 100644
--- a/tests/Feature/Pix/PixResourceTest.php
+++ b/tests/Feature/Pix/PixResourceTest.php
@@ -16,20 +16,24 @@
 use GuzzleHttp\Psr7\Response;
 
 beforeEach(function () {
-    $this->requestDto = CreatePixQrCodeRequest::make([
-        'amount' => 100,
-        'expiresIn' => 10,
-        'description' => 'abacate description',
-        'customer' => PixCustomerRequest::make([
-            'name' => 'customer name',
-            'cellphone' => '11982516627',
-            'email' => 'joe@doe.com',
-            'taxId' => '123.456.789-01',
-        ]),
-        'metadata' => PixMetadataRequest::make([
-            'externalId' => 'customer-id-123',
-        ]),
-    ]);
+    $this->requestDto = CreatePixQrCodeRequest::builder()
+        ->amount(100)
+        ->expiresIn(10)
+        ->description('abacate description')
+        ->customer(
+            PixCustomerRequest::builder()
+                ->name('customer name')
+                ->cellphone('11982516627')
+                ->email('joe@doe.com')
+                ->taxId('123.456.789-01')
+                ->build()
+        )
+        ->metadata(
+            PixMetadataRequest::builder()
+                ->externalId('customer-id-123')
+                ->build()
+        )
+        ->build();
 });
 
 it('should be able to create a Qr for pix', function (): void {
@@ -56,9 +60,7 @@
 
     $resource = new PixResource(client: $client);
 
-    $response = $resource->createQrCode(
-        $this->requestDto,
-    );
+    $response = $resource->createQrCode($this->requestDto);
 
     expect($response)->toBeInstanceOf(CreatePixQrCodeResponse::class)
         ->and($response->data->id)->toBe('pix_char_123456')
@@ -74,7 +76,6 @@
 });
 
 it('should throw exception when anything goes wrong', function () {
-
     $handler = new MockHandler([
         new ClientException(
             'Unauthorized',
diff --git a/tests/Unit/Billing/CreateBillingRequestBuilderTest.php b/tests/Unit/Billing/CreateBillingRequestBuilderTest.php
new file mode 100644
index 0000000..8133b33
--- /dev/null
+++ b/tests/Unit/Billing/CreateBillingRequestBuilderTest.php
@@ -0,0 +1,102 @@
+<?php
+
+declare(strict_types=1);
+
+use Basement\AbacatePay\Billing\Enum\BillingFrequencyEnum;
+use Basement\AbacatePay\Billing\Enum\BillingMethodEnum;
+use Basement\AbacatePay\Billing\Http\Request\CreateBillingRequest;
+use Basement\AbacatePay\Billing\Http\Request\ProductRequest;
+use Basement\AbacatePay\Customer\Http\Request\CustomerRequest;
+use Basement\AbacatePay\Exception\AbacatePayException;
+
+beforeEach(function () {
+    $this->product = ProductRequest::builder()
+        ->externalId('prod-123')
+        ->name('Curso PHP')
+        ->description('Curso completo de PHP moderno')
+        ->quantity(1)
+        ->price(15000)
+        ->build();
+
+    $this->customer = CustomerRequest::builder()
+        ->id('cust_abc123')
+        ->name('João Silva')
+        ->cellphone('+5511999999999')
+        ->email('joao@email.com')
+        ->taxId('12345678900')
+        ->build();
+});
+
+it('should build a valid CreateBillingRequest', function () {
+    $request = CreateBillingRequest::oneTime()
+        ->pix()
+        ->returnUrl('https://retorno.exemplo.com')
+        ->completionUrl('https://finalizacao.exemplo.com')
+        ->addProduct($this->product)
+        ->forCustomer($this->customer)
+        ->build();
+
+    expect($request)
+        ->toBeInstanceOf(CreateBillingRequest::class)
+        ->and($request->frequency)->toBe(BillingFrequencyEnum::OneTime)
+        ->and($request->methods)->toBe([BillingMethodEnum::Pix])
+        ->and($request->products)->toHaveCount(1)
+        ->and($request->customer->id)->toBe('cust_abc123')
+        ->and($request->allow_coupons)->toBeFalse()
+        ->and($request->coupons)->toBe([]);
+});
+
+it('should throw AbacatePayException when required fields are missing', function () {
+    expect(fn () => CreateBillingRequest::builder()->build())
+        ->toThrow(AbacatePayException::class, 'Missing required fields');
+});
+
+it('should throw AbacatePayException when both customer and customerId are set', function () {
+    $builder = CreateBillingRequest::oneTime()
+        ->pix()
+        ->returnUrl('https://retorno.exemplo.com')
+        ->completionUrl('https://finalizacao.exemplo.com')
+        ->addProduct($this->product)
+        ->forCustomer($this->customer)
+        ->forCustomerId('cust_conflict');
+
+    expect(fn () => $builder->build())
+        ->toThrow(InvalidArgumentException::class);
+});
+
+it('should allow optional fields to be omitted', function () {
+    $request = CreateBillingRequest::oneTime()
+        ->pix()
+        ->returnUrl('https://retorno.exemplo.com')
+        ->completionUrl('https://finalizacao.exemplo.com')
+        ->addProduct($this->product)
+        ->build();
+
+    expect($request)
+        ->toBeInstanceOf(CreateBillingRequest::class)
+        ->and($request->externalId)->toBeNull()
+        ->and($request->customerId)->toBeNull()
+        ->and($request->customer)->toBeNull()
+        ->and($request->coupons)->toBe([])
+        ->and($request->allow_coupons)->toBeFalse();
+});
+
+it('should accept multiple methods and products', function () {
+    $product2 = ProductRequest::builder()
+        ->externalId('prod-456')
+        ->name('Curso Laravel')
+        ->description('Aprenda Laravel com exemplos práticos')
+        ->quantity(1)
+        ->price(18000)
+        ->build();
+
+    $request = CreateBillingRequest::multipleTimes()
+        ->methods(BillingMethodEnum::Card, BillingMethodEnum::Pix)
+        ->returnUrl('https://retorno.exemplo.com')
+        ->completionUrl('https://finalizacao.exemplo.com')
+        ->products($this->product, $product2)
+        ->build();
+
+    expect($request->methods)->toBe([BillingMethodEnum::Card, BillingMethodEnum::Pix])
+        ->and($request->products)->toHaveCount(2);
+});
diff --git a/tests/Unit/Pix/CreatePixQrCodeRequestBuilderTest.php b/tests/Unit/Pix/CreatePixQrCodeRequestBuilderTest.php
new file mode 100644
index 0000000..4f7c780
--- /dev/null
+++ b/tests/Unit/Pix/CreatePixQrCodeRequestBuilderTest.php
@@ -0,0 +1,81 @@
+<?php
+
+declare(strict_types=1);
+
+use Basement\AbacatePay\Exception\AbacatePayException;
+use Basement\AbacatePay\Pix\Http\Request\CreatePixQrCodeRequest;
+use Basement\AbacatePay\Pix\Http\Request\PixCustomerRequest;
+use Basement\AbacatePay\Pix\Http\Request\PixMetadataRequest;
+
+it('builds a valid CreatePixQrCodeRequest', function () {
+    $customer = PixCustomerRequest::builder()
+        ->name('Maria')
+        ->cellphone('+5511999999999')
+        ->email('maria@email.com')
+        ->taxId('12345678900')
+        ->build();
+
+    $metadata = PixMetadataRequest::builder()
+        ->externalId('order-123')
+        ->build();
+
+    $request = CreatePixQrCodeRequest::builder()
+        ->amount(10000)
+        ->expiresIn(3600)
+        ->description('Pagamento de assinatura')
+        ->customer($customer)
+        ->metadata($metadata)
+        ->build();
+
+    expect($request)
+        ->toBeInstanceOf(CreatePixQrCodeRequest::class)
+        ->and($request->amount)->toBe(10000)
+        ->and($request->description)->toBe('Pagamento de assinatura')
+        ->and($request->customer->name)->toBe('Maria')
+        ->and($request->metadata->externalId)->toBe('order-123')
+        ->and($customer->toArray())->toBe([
+            'name' => 'Maria',
+            'cellphone' => '+5511999999999',
+            'email' => 'maria@email.com',
+            'taxId' => '12345678900',
+        ])
+        ->and($metadata->toArray())->toBe([
+            'externalId' => 'order-123',
+        ])
+        ->and($request->toArray())->toBe([
+            'amount' => 10000,
+            'expiresIn' => 3600,
+            'description' => 'Pagamento de assinatura',
+            'customer' => [
+                'name' => 'Maria',
+                'cellphone' => '+5511999999999',
+                'email' => 'maria@email.com',
+                'taxId' => '12345678900',
+            ],
+            'metadata' => [
+                'externalId' => 'order-123',
+            ],
+        ]);
+});
+
+it('should allow creating a QR code with only required fields', function (): void {
+    $request = CreatePixQrCodeRequest::builder()
+        ->amount(250)
+        ->build();
+
+    expect($request)
+        ->toBeInstanceOf(CreatePixQrCodeRequest::class)
+        ->and($request->amount)->toBe(250)
+        ->and($request->expiresIn)->toBeNull()
+        ->and($request->description)->toBeNull()
+        ->and($request->customer)->toBeNull()
+        ->and($request->metadata)->toBeNull();
+
+    $serialized = $request->toArray();
+
+    expect($serialized)->toBe(['amount' => 250]);
+});
+
+it('throws AbacatePayException when missing required fields', function () {
+    CreatePixQrCodeRequest::builder()->build();
+})->throws(AbacatePayException::class, 'Missing required fields');