diff --git a/Tests/Feature/Order/IndexOrdersTest.php b/Tests/Feature/Order/IndexOrdersTest.php
index c474337..55ac51a 100644
--- a/Tests/Feature/Order/IndexOrdersTest.php
+++ b/Tests/Feature/Order/IndexOrdersTest.php
@@ -35,8 +35,8 @@ public function index_orders(): void
     }
 
     /**
-     * @dataProvider orderFilterDataProvider
      * @test
+     * @dataProvider orderFilterDataProvider
      */
     public function index_orders_with_filter(string $method, mixed $value, string $queryKey, string $queryValue): void
     {
diff --git a/Tests/Feature/Order/Mock/OrderShowMockClient.php b/Tests/Feature/Order/Mock/OrderShowMockClient.php
index 238ef61..844514d 100644
--- a/Tests/Feature/Order/Mock/OrderShowMockClient.php
+++ b/Tests/Feature/Order/Mock/OrderShowMockClient.php
@@ -237,4 +237,25 @@ public function taxes(): self
 
         return $this;
     }
+
+    public function customFields(): self
+    {
+        $this->items();
+
+        $this->responseBody['data']['items'][0]['custom_fields'] = [
+            'id'              => 1,
+            'input'           => 'Bart',
+            'label'           => 'Wie is jouw contactpersoon?',
+        ];
+
+        $this->responseBody['data']['custom_fields'] = [
+            [
+                'id'              => 1,
+                'input'           => 'Bart',
+                'label'           => 'Wie is jouw contactpersoon?',
+            ],
+        ];
+
+        return $this;
+    }
 }
diff --git a/Tests/Feature/Order/ShowOrderTest.php b/Tests/Feature/Order/ShowOrderTest.php
index e3a793b..ea9819b 100644
--- a/Tests/Feature/Order/ShowOrderTest.php
+++ b/Tests/Feature/Order/ShowOrderTest.php
@@ -75,13 +75,14 @@ public function show_none_loaded_relationships(string $relation): void
     public static function relationsProvider(): array
     {
         return [
-            'billing'        => ['billing'],
-            'comments'       => ['comments'],
-            'totalDiscounts' => ['totalDiscounts'],
-            'items'          => ['items'],
-            'payment'        => ['payment'],
-            'tags'           => ['tags'],
-            'taxes'          => ['taxes'],
+            'billing'            => ['billing'],
+            'comments'           => ['comments'],
+            'customFields'       => ['customFields'],
+            'totalDiscounts'     => ['totalDiscounts'],
+            'items'              => ['items'],
+            'payment'            => ['payment'],
+            'tags'               => ['tags'],
+            'taxes'              => ['taxes'],
         ];
     }
 
@@ -135,6 +136,7 @@ public function show_order_billing_basic(): void
         static::assertSame(TaxExempt::NONE, $contact->taxExempt());
 
         $address = $billing->address();
+
         static::assertNull($address->city());
         static::assertNull($address->country());
         static::assertNull($address->street());
@@ -183,11 +185,13 @@ public function show_order_unknown_tax_exempt(): void
                 'website'       => null,
                 'vat_id_number' => null,
             ], ]);
+
         $service = new OrderService($client);
 
         $order = $service->find(1);
 
         $contact = $order->billing()->contact();
+
         static::assertEquals(TaxExempt::UNKNOWN, $contact->taxExempt());
     }
 
@@ -200,6 +204,7 @@ public function show_order_comments(): void
         $order = $service->find(1);
 
         $comment = $order->comments()[0];
+
         static::assertSame('2019-01-16 12:00:00', $comment->createdAt()->format('Y-m-d H:i:s'));
         static::assertSame(1, $comment->id());
         static::assertSame('2019-01-17 12:10:00', $comment->updatedAt()->format('Y-m-d H:i:s'));
@@ -294,12 +299,34 @@ public function show_order_taxes(): void
         static::assertSame(21., $order->taxes()[0]->rate()->percentage());
 
         $tax = $order->items()[0]->tax();
+
         static::assertSame(10., $tax->amount());
         static::assertSame(CountryCode::NL, $tax->rate()->country());
         static::assertSame(57, $tax->rate()->id());
         static::assertSame(21., $tax->rate()->percentage());
     }
 
+    // /** @test */
+    // public function show_order_custom_fields(): void
+    // {
+    //     $client  = (new OrderShowMockClient())->customFields();
+    //     $service = new OrderService($client);
+
+    //     $order = $service->find(1);
+
+    //     static::assertSame(10., $order->customFields()[0]->amount());
+    //     static::assertSame(CountryCode::NL, $order->taxes()[0]->rate()->country());
+    //     static::assertSame(57, $order->taxes()[0]->rate()->id());
+    //     static::assertSame(21., $order->taxes()[0]->rate()->percentage());
+
+    //     $tax = $order->items()[0]->tax();
+
+    //     static::assertSame(10., $tax->amount());
+    //     static::assertSame(CountryCode::NL, $tax->rate()->country());
+    //     static::assertSame(57, $tax->rate()->id());
+    //     static::assertSame(21., $tax->rate()->percentage());
+    // }
+
     /** @test */
     public function show_order_discount(): void
     {
@@ -318,6 +345,7 @@ public function show_order_with_empty_source(): void
         $client  = (new OrderShowMockClient([
             'source' => null,
         ]));
+
         $service = new OrderService($client);
 
         $order = $service->find(1);
diff --git a/Tests/Feature/Order/StoreOrderTest.php b/Tests/Feature/Order/StoreOrderTest.php
index 8694b55..c5e6f7d 100644
--- a/Tests/Feature/Order/StoreOrderTest.php
+++ b/Tests/Feature/Order/StoreOrderTest.php
@@ -130,7 +130,7 @@ public function convert_item_to_body(): void
 
     /**
      * @test
-     * @dataProvider convert_order_fields_data_provider
+     * @dataProvider convertOrderFieldsDataProvider
      */
     public function convert_order_fields(string $method, string $bodyField, $value): void
     {
@@ -141,7 +141,7 @@ public function convert_order_fields(string $method, string $bodyField, $value):
         static::assertEquals($value, $body[$bodyField]);
     }
 
-    public static function convert_order_fields_data_provider(): array
+    public static function convertOrderFieldsDataProvider(): array
     {
         return [
             'isHidden' => [
diff --git a/src/Director/BodyTo/BodyToCustomField.php b/src/Director/BodyTo/BodyToCustomField.php
new file mode 100644
index 0000000..7e23382
--- /dev/null
+++ b/src/Director/BodyTo/BodyToCustomField.php
@@ -0,0 +1,18 @@
+<?php
+
+declare(strict_types=1);
+
+namespace PlugAndPay\Sdk\Director\BodyTo;
+
+use PlugAndPay\Sdk\Entity\CustomField;
+
+class BodyToCustomField
+{
+    public static function build(array $data): CustomField
+    {
+        return (new CustomField())
+            ->setId($data['id'])
+            ->setInput($data['input'])
+            ->setLabel($data['label']);
+    }
+}
diff --git a/src/Director/BodyTo/BodyToItems.php b/src/Director/BodyTo/BodyToItems.php
index 0a3a370..920c830 100644
--- a/src/Director/BodyTo/BodyToItems.php
+++ b/src/Director/BodyTo/BodyToItems.php
@@ -16,15 +16,18 @@ class BodyToItems
     public static function build(array $data): array
     {
         $result = [];
+
         foreach ($data as $itemData) {
-            $item = (new ItemInternal())
+            $item = (new ItemInternal());
+
+            $item
                 ->setId($itemData['id'])
+                ->setType($itemData['type'] ? ItemType::from($itemData['type']) : ItemType::STANDARD)
                 ->setProductId($itemData['product_id'])
                 ->setLabel($itemData['label'])
                 ->setQuantity($itemData['quantity'])
                 ->setAmount((float) $itemData['amount'])
-                ->setAmountWithTax((float) $itemData['amount_with_tax'])
-                ->setType($itemData['type'] ? ItemType::from($itemData['type']) : ItemType::STANDARD);
+                ->setAmountWithTax((float) $itemData['amount_with_tax']);
 
             if (isset($itemData['discounts'])) {
                 $item->setDiscounts(BodyToDiscounts::buildMany($itemData['discounts']));
@@ -34,6 +37,10 @@ public static function build(array $data): array
                 $item->setTax(BodyToTax::build($itemData['tax']));
             }
 
+            if (isset($itemData['custom_fields'])) {
+                $item->setCustomFields(BodyToCustomField::build($itemData['custom_fields']));
+            }
+
             $result[] = $item;
         }
 
diff --git a/src/Director/BodyTo/BodyToOrder.php b/src/Director/BodyTo/BodyToOrder.php
index 6fde6f7..c0364fe 100644
--- a/src/Director/BodyTo/BodyToOrder.php
+++ b/src/Director/BodyTo/BodyToOrder.php
@@ -17,24 +17,27 @@ class BodyToOrder
 {
     /**
      * @throws DecodeResponseException
-     * @throws Exception
      */
     public static function build(array $data): Order
     {
-        $order = (new OrderInternal(false))
+        $order = new OrderInternal(
+            allowEmptyRelations: false
+        );
+
+        $order
             ->setCreatedAt(self::date($data, 'created_at'))
             ->setDeletedAt($data['deleted_at'] ? self::date($data, 'deleted_at') : null)
             ->setFirst($data['is_first'])
-            ->setHidden($data['is_hidden'])
             ->setId($data['id'])
             ->setInvoiceNumber($data['invoice_number'])
             ->setInvoiceStatus(InvoiceStatus::from($data['invoice_status']))
-            ->setMode(Mode::from($data['mode']))
             ->setReference($data['reference'])
             ->setSource(Source::tryFrom($data['source'] ?? '') ?? Source::UNKNOWN)
+            ->setUpdatedAt(self::date($data, 'updated_at'))
+            ->setHidden($data['is_hidden'])
+            ->setMode(Mode::from($data['mode']))
             ->setAmount((float) $data['amount'])
-            ->setAmountWithTax((float) $data['amount_with_tax'])
-            ->setUpdatedAt(self::date($data, 'updated_at'));
+            ->setAmountWithTax((float) $data['amount_with_tax']);
 
         if (isset($data['billing'])) {
             $order->setBilling(BodyToOrderBilling::build($data['billing']));
diff --git a/src/Entity/CustomField.php b/src/Entity/CustomField.php
new file mode 100644
index 0000000..50dcf99
--- /dev/null
+++ b/src/Entity/CustomField.php
@@ -0,0 +1,49 @@
+<?php
+
+declare(strict_types=1);
+
+namespace PlugAndPay\Sdk\Entity;
+
+class CustomField
+{
+    private int $id;
+
+    private string $input;
+    private string $label;
+
+    public function id(): int
+    {
+        return $this->id;
+    }
+
+    public function setId(int $id): self
+    {
+        $this->id = $id;
+
+        return $this;
+    }
+
+    public function input(): string
+    {
+        return $this->input;
+    }
+
+    public function setInput(string $input): self
+    {
+        $this->input = $input;
+
+        return $this;
+    }
+
+    public function label(): string
+    {
+        return $this->label;
+    }
+
+    public function setLabel(string $label): self
+    {
+        $this->label = $label;
+
+        return $this;
+    }
+}
diff --git a/src/Entity/Item.php b/src/Entity/Item.php
index 7a91859..0450a22 100644
--- a/src/Entity/Item.php
+++ b/src/Entity/Item.php
@@ -5,6 +5,7 @@
 namespace PlugAndPay\Sdk\Entity;
 
 use PlugAndPay\Sdk\Enum\ItemType;
+use PlugAndPay\Sdk\Exception\RelationNotLoadedException;
 use PlugAndPay\Sdk\Traits\ValidatesFieldMethods;
 
 class Item
@@ -13,15 +14,22 @@ class Item
 
     protected float $amount;
     protected float $amountWithTax;
+
     /** @var Discount[] */
     protected array $discounts;
+
     protected int $id;
     protected string $label;
+
     protected int $productId;
     protected int $quantity;
+
     protected Tax $tax;
     protected ItemType $type;
 
+    /** @var CustomField[] */
+    protected array $customFields;
+
     public function id(): int
     {
         return $this->id;
@@ -115,4 +123,16 @@ public function type(): ItemType
     {
         return $this->type;
     }
+
+    /**
+     * @throws RelationNotLoadedException
+     */
+    public function customFields(): array
+    {
+        if (!isset($this->customFields)) {
+            throw new RelationNotLoadedException('customFields');
+        }
+
+        return $this->customFields;
+    }
 }
diff --git a/src/Entity/ItemInternal.php b/src/Entity/ItemInternal.php
index c965ed4..835e1f5 100644
--- a/src/Entity/ItemInternal.php
+++ b/src/Entity/ItemInternal.php
@@ -40,4 +40,14 @@ public function setType(ItemType $type): self
 
         return $this;
     }
+
+    /**
+     * @internal
+     */
+    public function setCustomFields(CustomField $customFields): self
+    {
+        $this->customFields = $customFields;
+
+        return $this;
+    }
 }
diff --git a/src/Entity/Order.php b/src/Entity/Order.php
index b74442a..13c17ab 100644
--- a/src/Entity/Order.php
+++ b/src/Entity/Order.php
@@ -15,31 +15,47 @@ class Order
 {
     use HasDynamicFields;
 
+    protected int $id;
+
     protected bool $allowEmptyRelations;
+
     protected float $amount;
     protected float $amountWithTax;
+
     protected OrderBilling $billing;
+
     /** @var Comment[] */
     protected array $comments;
+
     protected DateTimeImmutable $createdAt;
-    protected ?DateTimeImmutable $deletedAt;
+    protected DateTimeImmutable | null $deletedAt;
+
     /** @var Discount[] */
     protected array $totalDiscounts;
+
     protected bool $first;
     protected bool $hidden;
-    protected int $id;
-    protected ?string $invoiceNumber;
+
+    protected string | null $invoiceNumber;
+
     protected InvoiceStatus $invoiceStatus;
+
     /** @var Item[] */
     protected array $items;
+
     protected Mode $mode;
+
     protected Payment $payment;
     protected string $reference;
+
     protected Source $source;
+
     /** @var string[] */
     protected array $tags;
+
     /** @var Tax[] */
     protected array $taxes;
+
     protected DateTimeImmutable $updatedAt;
 
     public function __construct(bool $allowEmptyRelations = true)
@@ -123,7 +139,7 @@ public function createdAt(): DateTimeImmutable
         return $this->createdAt;
     }
 
-    public function deletedAt(): ?DateTimeImmutable
+    public function deletedAt(): DateTimeImmutable | null
     {
         return $this->deletedAt;
     }
@@ -140,14 +156,11 @@ public function totalDiscounts(): array
         return $this->totalDiscounts;
     }
 
-    public function invoiceNumber(): ?string
+    public function setTotalDiscounts(array $totalDiscounts): self
     {
-        return $this->invoiceNumber;
-    }
+        $this->totalDiscounts = $totalDiscounts;
 
-    public function invoiceStatus(): InvoiceStatus
-    {
-        return $this->invoiceStatus;
+        return $this;
     }
 
     public function isFirst(): bool
@@ -167,6 +180,16 @@ public function setHidden(bool $hidden): self
         return $this;
     }
 
+    public function invoiceNumber(): string | null
+    {
+        return $this->invoiceNumber;
+    }
+
+    public function invoiceStatus(): InvoiceStatus
+    {
+        return $this->invoiceStatus;
+    }
+
     /**
      * @throws RelationNotLoadedException
      */
@@ -262,6 +285,13 @@ public function taxes(): array
         return $this->taxes;
     }
 
+    public function setTaxes(array $taxes): self
+    {
+        $this->taxes = $taxes;
+
+        return $this;
+    }
+
     public function updatedAt(): DateTimeImmutable
     {
         return $this->updatedAt;
diff --git a/src/Entity/OrderInternal.php b/src/Entity/OrderInternal.php
index cda969b..3e42716 100644
--- a/src/Entity/OrderInternal.php
+++ b/src/Entity/OrderInternal.php
@@ -26,7 +26,7 @@ public function setCreatedAt(DateTimeImmutable $createdAt): self
     /**
      * @internal
      */
-    public function setDeletedAt(?DateTimeImmutable $deletedAt): self
+    public function setDeletedAt(DateTimeImmutable | null $deletedAt): self
     {
         $this->deletedAt = $deletedAt;
 
@@ -56,7 +56,7 @@ public function setId(int $id): self
     /**
      * @internal
      */
-    public function setInvoiceNumber(?string $invoiceNumber): self
+    public function setInvoiceNumber(string | null $invoiceNumber): self
     {
         $this->invoiceNumber = $invoiceNumber;
 
@@ -93,26 +93,6 @@ public function setSource(Source $source): self
         return $this;
     }
 
-    /**
-     * @internal
-     */
-    public function setTaxes(array $taxes): self
-    {
-        $this->taxes = $taxes;
-
-        return $this;
-    }
-
-    /**
-     * @internal
-     */
-    public function setTotalDiscounts(array $totalDiscounts): self
-    {
-        $this->totalDiscounts = $totalDiscounts;
-
-        return $this;
-    }
-
     /**
      * @internal
      */
diff --git a/src/Enum/OrderIncludes.php b/src/Enum/OrderIncludes.php
index d9aac26..0381b45 100644
--- a/src/Enum/OrderIncludes.php
+++ b/src/Enum/OrderIncludes.php
@@ -4,11 +4,12 @@
 
 enum OrderIncludes: string
 {
-    case BILLING   = 'billing';
-    case COMMENTS  = 'comments';
-    case DISCOUNTS = 'discounts';
-    case ITEMS     = 'items';
-    case PAYMENT   = 'payment';
-    case TAGS      = 'tags';
-    case TAXES     = 'taxes';
+    case BILLING        = 'billing';
+    case COMMENTS       = 'comments';
+    case CUSTOM_FIELDS  = 'custom_fields';
+    case DISCOUNTS      = 'discounts';
+    case ITEMS          = 'items';
+    case PAYMENT        = 'payment';
+    case TAGS           = 'tags';
+    case TAXES          = 'taxes';
 }
diff --git a/src/Service/OrderService.php b/src/Service/OrderService.php
index f089286..fbb5b92 100644
--- a/src/Service/OrderService.php
+++ b/src/Service/OrderService.php
@@ -5,7 +5,6 @@
 namespace PlugAndPay\Sdk\Service;
 
 use PlugAndPay\Sdk\Contract\ClientInterface;
-use PlugAndPay\Sdk\Contract\ClientPatchInterface;
 use PlugAndPay\Sdk\Director\BodyTo\BodyToOrder;
 use PlugAndPay\Sdk\Director\ToBody\OrderToBody;
 use PlugAndPay\Sdk\Entity\Order;
@@ -17,7 +16,8 @@
 
 class OrderService
 {
-    private ClientPatchInterface $client;
+    private ClientInterface $client;
+
     /** @var string[] */
     private array $includes = [];