diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index c2402db..46f79e2 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -12,15 +12,13 @@ jobs:
 
     strategy:
       matrix:
-        php-versions: ['7.4', '8.0', '8.1', '8.2']
+        php-versions: ['7.4', '8.0', '8.1', '8.2', '8.3']
 
     steps:
-      - uses: actions/checkout@v2
-        with:
-          ref: ${{ github.head_ref }}
+      - uses: actions/checkout@v4
 
       - name: Cache composer dependencies
-        uses: actions/cache@v2
+        uses: actions/cache@v4
         with:
           path: vendor
           key: composer-${{ hashFiles('composer.lock') }}
diff --git a/src/RequestModels/Message.php b/src/RequestModels/Message.php
index 6bc26b6..509d206 100644
--- a/src/RequestModels/Message.php
+++ b/src/RequestModels/Message.php
@@ -21,6 +21,7 @@ class Message
     protected string $encoding = self::ENCODING_GSM7;
     protected ?string $messageId = null;
     protected ?string $countryHint = null;
+    protected ?int $msisdnCooldownInMinutes = null;
 
     /**
      * @var mixed
@@ -107,6 +108,13 @@ public function setCountryHint(string $countryHint): self
         return $this;
     }
 
+    public function setMsisdnCooldownInMinutes(?int $msisdnCooldownInMinutes): self
+    {
+        $this->msisdnCooldownInMinutes = $msisdnCooldownInMinutes;
+
+        return $this;
+    }
+
     public function toArray(): array
     {
         return [
@@ -123,6 +131,7 @@ public function toArray(): array
             'respectBlacklist' => $this->respectBlacklist,
             'statusCallbackUrl' => $this->statusCallbackUrl,
             'encoding' => $this->encoding,
+            'msisdnCooldownInMinutes' => $this->msisdnCooldownInMinutes,
         ];
     }
 
@@ -180,4 +189,9 @@ public function getCountryHint(): ?string
     {
         return $this->countryHint;
     }
+
+    public function getMsisdnCooldownInMinutes(): ?int
+    {
+        return $this->msisdnCooldownInMinutes;
+    }
 }
diff --git a/tests/Unit/Endpoints/MessagesApiTest.php b/tests/Unit/Endpoints/MessagesApiTest.php
index 1f3a28a..ba0be51 100644
--- a/tests/Unit/Endpoints/MessagesApiTest.php
+++ b/tests/Unit/Endpoints/MessagesApiTest.php
@@ -137,6 +137,7 @@ public function test_sends_a_single_message_with_all_possible_fields()
                         'respectBlacklist' => false,
                         'statusCallbackUrl' => 'https://example.com/inmobile/callback',
                         'encoding' => Message::ENCODING_UCS2,
+                        'msisdnCooldownInMinutes' => null,
                     ], $payload['messages'][0]);
 
                     return true;
diff --git a/tests/Unit/RequestModels/MessageTest.php b/tests/Unit/RequestModels/MessageTest.php
index d023774..b99a6aa 100644
--- a/tests/Unit/RequestModels/MessageTest.php
+++ b/tests/Unit/RequestModels/MessageTest.php
@@ -21,7 +21,8 @@ public function test_create_a_message()
             ->flash()
             ->ignoreBlacklist()
             ->setEncoding(Message::ENCODING_GSM7)
-            ->setStatusCallbackUrl('https://example.com/callback');
+            ->setStatusCallbackUrl('https://example.com/callback')
+            ->setMsisdnCooldownInMinutes(60);
 
         $this->assertEquals('Hello World', $message->getText());
         $this->assertEquals(4512345678, $message->getRecipient());
@@ -34,6 +35,7 @@ public function test_create_a_message()
         $this->assertFalse($message->getRespectBlacklist());
         $this->assertEquals(Message::ENCODING_GSM7, $message->getEncoding());
         $this->assertEquals('https://example.com/callback', $message->getStatusCallbackUrl());
+        $this->assertEquals(60, $message->getMsisdnCooldownInMinutes());
     }
 
     public function test_convert_to_array()
@@ -49,7 +51,8 @@ public function test_convert_to_array()
             ->flash()
             ->ignoreBlacklist()
             ->setEncoding(Message::ENCODING_GSM7)
-            ->setStatusCallbackUrl('https://example.com/callback');
+            ->setStatusCallbackUrl('https://example.com/callback')
+            ->setMsisdnCooldownInMinutes(60);
 
         $this->assertEquals([
             'to' => '4512345678',
@@ -63,6 +66,7 @@ public function test_convert_to_array()
             'respectBlacklist' => false,
             'statusCallbackUrl' => 'https://example.com/callback',
             'encoding' => Message::ENCODING_GSM7,
+            'msisdnCooldownInMinutes' => 60,
         ], $message->toArray());
     }
 }