diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3b9d65e..05a8247 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,8 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/) and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
+### Fixed
+- sending/scheduling smses in large amount 
 ### Added
 - PHP-8.3 support
 
diff --git a/src/Feature/Sms/Bag/ScheduleSmssBag.php b/src/Feature/Sms/Bag/ScheduleSmssBag.php
index b6fda24..6d2afc3 100644
--- a/src/Feature/Sms/Bag/ScheduleSmssBag.php
+++ b/src/Feature/Sms/Bag/ScheduleSmssBag.php
@@ -29,7 +29,7 @@
 #[\AllowDynamicProperties]
 class ScheduleSmssBag
 {
-    /** @var array */
+    /** @var array|string */
     public $to;
 
     /** @var DateTimeInterface */
diff --git a/src/Feature/Sms/Bag/SendSmssBag.php b/src/Feature/Sms/Bag/SendSmssBag.php
index 53dc09b..5a48c72 100644
--- a/src/Feature/Sms/Bag/SendSmssBag.php
+++ b/src/Feature/Sms/Bag/SendSmssBag.php
@@ -29,7 +29,7 @@
 #[\AllowDynamicProperties]
 class SendSmssBag
 {
-    /** @var array */
+    /** @var array|string */
     public $to;
 
     /** @var string */
diff --git a/src/Feature/Sms/SmsHttpFeature.php b/src/Feature/Sms/SmsHttpFeature.php
index 10dea8b..b2e2299 100644
--- a/src/Feature/Sms/SmsHttpFeature.php
+++ b/src/Feature/Sms/SmsHttpFeature.php
@@ -110,6 +110,8 @@ public function sendFlashSmsToGroup(SendSmsToGroupBag $sendSmsToGroupBag): array
 
     public function sendSmss(SendSmssBag $sendSmssBag): array
     {
+        $sendSmssBag->to = implode(',', $sendSmssBag->to);
+
         return array_map(
             [$this->dataFactoryProvider->provideSmsFactory(), 'createFromObject'],
             $this->makeRequest($sendSmssBag)->list
@@ -118,6 +120,8 @@ public function sendSmss(SendSmssBag $sendSmssBag): array
 
     public function sendFlashSmss(SendSmssBag $sendSmssBag): array
     {
+        $sendSmssBag->to = implode(',', $sendSmssBag->to);
+
         return array_map(
             [$this->dataFactoryProvider->provideSmsFactory(), 'createFromObject'],
             $this->makeRequest($sendSmssBag)->list
@@ -146,6 +150,7 @@ public function scheduleSms(ScheduleSmsBag $scheduleSmsBag): Sms
 
     public function scheduleSmss(ScheduleSmssBag $scheduleSmssBag): array
     {
+        $scheduleSmssBag->to = implode(',', $scheduleSmssBag->to);
         $scheduleSmssBag->dateValidate = true;
 
         return array_map(
diff --git a/src/Infrastructure/RequestMapper/LegacyRequestMapper.php b/src/Infrastructure/RequestMapper/LegacyRequestMapper.php
index c59e314..b881e30 100644
--- a/src/Infrastructure/RequestMapper/LegacyRequestMapper.php
+++ b/src/Infrastructure/RequestMapper/LegacyRequestMapper.php
@@ -34,9 +34,7 @@ private function createRequest(
         array $builtInParameters,
         array $userParameters
     ): Request {
-        $builtInParameters['format'] = 'json';
-
-        $parameters = new QueryParametersData($builtInParameters, $userParameters);
+        $parameters = new QueryParametersData(['format' => 'json'] + $builtInParameters, $userParameters);
 
         return new Request($method, $path, $this->queryFormatter->format($parameters));
     }
diff --git a/tests/Fixture/PhoneNumberFixture.php b/tests/Fixture/PhoneNumberFixture.php
index 2ab2941..9f06e1f 100644
--- a/tests/Fixture/PhoneNumberFixture.php
+++ b/tests/Fixture/PhoneNumberFixture.php
@@ -20,4 +20,9 @@ public static function anyValidMobile(): string
     {
         return (string)((int)self::$validMobile + self::$i++);
     }
+
+    public static function xValidMobile(int $x): array
+    {
+        return array_map(function () {return self::anyValidMobile();}, range(1, $x));
+    }
 }
diff --git a/tests/Integration/Feature/Sms/SmsFeatureTest.php b/tests/Integration/Feature/Sms/SmsFeatureTest.php
index e78a420..c5051f8 100644
--- a/tests/Integration/Feature/Sms/SmsFeatureTest.php
+++ b/tests/Integration/Feature/Sms/SmsFeatureTest.php
@@ -82,12 +82,12 @@ public function it_should_send_flash_sms()
     public function it_should_send_smss()
     {
         $smsFeature = self::$smsapiService->smsFeature();
-        $sendSmssBag = $this->givenSmssToSend();
+        $sendSmssBag = $this->givenSmssToSend(2);
         $sendSmssBag->test = true;
 
         $results = $smsFeature->sendSmss($sendSmssBag);
 
-        $this->assertCount(count($sendSmssBag->to), $results);
+        $this->assertCount(2, $results);
     }
 
     /**
@@ -96,12 +96,12 @@ public function it_should_send_smss()
     public function it_should_send_flash_smss()
     {
         $smsFeature = self::$smsapiService->smsFeature();
-        $sendSmssBag = $this->givenSmssToSend();
+        $sendSmssBag = $this->givenSmssToSend(2);
         $sendSmssBag->test = true;
 
         $results = $smsFeature->sendFlashSmss($sendSmssBag);
 
-        $this->assertCount(count($sendSmssBag->to), $results);
+        $this->assertCount(2, $results);
     }
 
     /**
@@ -110,7 +110,7 @@ public function it_should_send_flash_smss()
     public function it_should_not_receive_content_details_for_smss()
     {
         $smsFeature = self::$smsapiService->smsFeature();
-        $sendSmsesBag = $this->givenSmssToSend();
+        $sendSmsesBag = $this->givenSmssToSend(2);
         $sendSmsesBag->test = true;
 
         /** @var Sms[] $results */
@@ -142,12 +142,12 @@ public function it_should_schedule_sms()
     public function it_should_schedule_smss()
     {
         $smsFeature = self::$smsapiService->smsFeature();
-        $scheduleSmssBag = $this->givenSmssToSchedule();
+        $scheduleSmssBag = $this->givenSmssToSchedule(2);
         $scheduleSmssBag->test = true;
 
         $results = $smsFeature->scheduleSmss($scheduleSmssBag);
 
-        $this->assertCount(count($scheduleSmssBag->to), $results);
+        $this->assertCount(2, $results);
     }
 
     /**
@@ -171,7 +171,7 @@ public function it_should_schedule_flash_sms()
     public function it_should_delete_scheduled_smss()
     {
         $smsFeature = self::$smsapiService->smsFeature();
-        $scheduleSmssBag = $this->givenSmssToSchedule();
+        $scheduleSmssBag = $this->givenSmssToSchedule(2);
 
         $results = $smsFeature->scheduleSmss($scheduleSmssBag);
         $smsIds = array_map(function (Sms $sms) {
@@ -190,12 +190,9 @@ private function givenSmsToSend(): SendSmsBag
         return SendSmsBag::withMessage($someReceiver, 'some message');
     }
 
-    private function givenSmssToSend(): SendSmssBag
+    private function givenSmssToSend(int $x): SendSmssBag
     {
-        $receivers = [
-            PhoneNumberFixture::anyValidMobile(),
-            PhoneNumberFixture::anyValidMobile(),
-        ];
+        $receivers = PhoneNumberFixture::xValidMobile($x);
         return SendSmssBag::withMessage($receivers, 'some message');
     }
 
@@ -206,13 +203,10 @@ private function givenSmsToSchedule(): ScheduleSmsBag
         return ScheduleSmsBag::withMessage($someDate, $someReceiver, 'some message');
     }
 
-    private function givenSmssToSchedule(): ScheduleSmssBag
+    private function givenSmssToSchedule(int $x): ScheduleSmssBag
     {
         $someDate = new DateTime('+1 day noon');
-        $receivers = [
-            PhoneNumberFixture::anyValidMobile(),
-            PhoneNumberFixture::anyValidMobile(),
-        ];
+        $receivers = PhoneNumberFixture::xValidMobile($x);
         return ScheduleSmssBag::withMessage($someDate, $receivers, 'some message');
     }
 }
diff --git a/tests/Unit/Infrastructure/RequestMapper/LegacyRequestMapperTest.php b/tests/Unit/Infrastructure/RequestMapper/LegacyRequestMapperTest.php
index 63f910f..9b5246a 100644
--- a/tests/Unit/Infrastructure/RequestMapper/LegacyRequestMapperTest.php
+++ b/tests/Unit/Infrastructure/RequestMapper/LegacyRequestMapperTest.php
@@ -25,10 +25,69 @@ public function init()
     /**
      * @test
      */
-    public function it_should_create_post_request_with_parameters()
+    public function it_should_use_path_as_request_uri()
     {
         $path = 'anyPath';
 
+        $request = $this->mapper->map($path, []);
+
+        $this->assertEquals($path, $request->getUri());
+    }
+
+    /**
+     * @test
+     */
+    public function it_should_send_request_as_post()
+    {
+        $request = $this->mapper->map('anyPath', []);
+
+        $this->assertEquals(RequestHttpMethod::POST, $request->getMethod());
+    }
+
+    /**
+     * @test
+     */
+    public function it_should_always_set_format_json_parameter()
+    {
+        $builtInParameters = [];
+        $userParameters = [];
+
+        $request = $this->mapper->map('anyPath', $builtInParameters, $userParameters);
+
+        $this->assertEquals('format=json', $request->getBody());
+    }
+
+    /**
+     * @test
+     */
+    public function it_should_prepend_format_parameter_to_built_in_parameters_when_none()
+    {
+        $builtInParameters = [];
+        $userParameters = ['any2' => 'any'];
+
+        $request = $this->mapper->map('anyPath', $builtInParameters, $userParameters);
+
+        $this->assertEquals('format=json&any2=any', $request->getBody());
+    }
+
+    /**
+     * @test
+     */
+    public function it_should_prepend_format_parameter_to_built_in_parameters_when_set()
+    {
+        $builtInParameters = ['any1' => 'any'];
+        $userParameters = [];
+
+        $request = $this->mapper->map('anyPath', $builtInParameters, $userParameters);
+
+        $this->assertEquals('format=json&any1=any', $request->getBody());
+    }
+
+    /**
+     * @test
+     */
+    public function it_should_merge_both_built_in_and_user_parameters()
+    {
         $builtInParameters = [
             'any1' => 'any',
         ];
@@ -36,11 +95,8 @@ public function it_should_create_post_request_with_parameters()
             'any2' => 'any',
         ];
 
-        $request = $this->mapper->map($path, $builtInParameters, $userParameters);
-
-        $this->assertEquals($path, $request->getUri());
-        $this->assertEquals(RequestHttpMethod::POST, $request->getMethod());
+        $request = $this->mapper->map('anyPath', $builtInParameters, $userParameters);
 
-        $this->assertEquals('any1=any&format=json&any2=any', $request->getBody());
+        $this->assertEquals('format=json&any1=any&any2=any', $request->getBody());
     }
 }