diff --git a/MyNumberNET.sln b/MyNumberNET.sln
index de907df..d0d01ae 100644
--- a/MyNumberNET.sln
+++ b/MyNumberNET.sln
@@ -8,6 +8,8 @@ Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "MyNumberNET_CLI", "MyNumber
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "MyNumberNET_Test", "MyNumberNET_Test\MyNumberNET_Test.csproj", "{0EE82E05-BD36-4024-BC61-A9B56E97E6B8}"
 EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "MyNumberNET_ApiServer", "MyNumberNET_ApiServer\MyNumberNET_ApiServer.csproj", "{5ABBBF4C-8CD9-405F-B2B4-2CD71A97CE1B}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -26,6 +28,10 @@ Global
 		{0EE82E05-BD36-4024-BC61-A9B56E97E6B8}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{0EE82E05-BD36-4024-BC61-A9B56E97E6B8}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{0EE82E05-BD36-4024-BC61-A9B56E97E6B8}.Release|Any CPU.Build.0 = Release|Any CPU
+		{5ABBBF4C-8CD9-405F-B2B4-2CD71A97CE1B}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{5ABBBF4C-8CD9-405F-B2B4-2CD71A97CE1B}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{5ABBBF4C-8CD9-405F-B2B4-2CD71A97CE1B}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{5ABBBF4C-8CD9-405F-B2B4-2CD71A97CE1B}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
diff --git a/MyNumberNET/MyNumber.cs b/MyNumberNET/MyNumber.cs
index 6e83afb..a130121 100644
--- a/MyNumberNET/MyNumber.cs
+++ b/MyNumberNET/MyNumber.cs
@@ -40,13 +40,18 @@ public static int CalculateCheckDigits(int[] number)
                 throw new MyNumberMalformedException("Malformed sequence. Must be 11 digits.");
             if (Array.Exists(number, n => n < 0 || n > 9))
                 throw new MyNumberMalformedException("All digits must be between 0 and 9.");
-            Array.Reverse(number);
+            
+            // Calculate check digit using the official My Number algorithm
+            // Process digits from right to left with specific weights
+            // Array indexing: number[11-n] safely accesses indices 10,9,8,...,0 for n=1,2,3,...,11
+            // This avoids Array.Reverse() while maintaining correct algorithm behavior
             var sum = 0;
+            // First loop: rightmost 6 digits (indices 10,9,8,7,6,5) with weights 2,3,4,5,6,7
             for (var n = 1; n < 7; n++)
-                sum += (n + 1) * number[n - 1];
+                sum += (n + 1) * number[11 - n];
+            // Second loop: leftmost 5 digits (indices 4,3,2,1,0) with weights 2,3,4,5,6
             for (var n = 7; n < 12; n++)
-                sum += (n - 5) * number[n - 1];
-            Array.Reverse(number);
+                sum += (n - 5) * number[11 - n];
             if (sum % 11 <= 1)
                 return 0;
             return 11 - sum % 11;
diff --git a/MyNumberNET_ApiServer/Controllers/MyNumberController.cs b/MyNumberNET_ApiServer/Controllers/MyNumberController.cs
index 1f88367..a9c197c 100644
--- a/MyNumberNET_ApiServer/Controllers/MyNumberController.cs
+++ b/MyNumberNET_ApiServer/Controllers/MyNumberController.cs
@@ -18,6 +18,13 @@ public class MyNumberController : ControllerBase
         [HttpPost("verify")]
         public ActionResult<bool> Verify([FromBody] int[] number)
         {
+            // Input validation before calling business logic
+            if (number == null)
+                return BadRequest("Input array is null.");
+            if (number.Length != 12)
+                return BadRequest("Malformed sequence. Must be 12 digits.");
+            if (number.Any(n => n < 0 || n > 9))
+                return BadRequest("All digits must be between 0 and 9.");
             try
             {
                 bool isValid = MyNumber.VerifyNumber(number);
@@ -37,6 +44,13 @@ public ActionResult<bool> Verify([FromBody] int[] number)
         [HttpPost("checkdigit")]
         public ActionResult<int> CheckDigit([FromBody] int[] number)
         {
+            // Input validation before calling business logic
+            if (number == null)
+                return BadRequest("Input array is null.");
+            if (number.Length != 11)
+                return BadRequest("Malformed sequence. Must be 11 digits.");
+            if (number.Any(n => n < 0 || n > 9))
+                return BadRequest("All digits must be between 0 and 9.");
             try
             {
                 int checkDigit = MyNumber.CalculateCheckDigits(number);
diff --git a/MyNumberNET_CLI/MyNumberNET_CLI.csproj b/MyNumberNET_CLI/MyNumberNET_CLI.csproj
index a6b14b9..67fa9d0 100644
--- a/MyNumberNET_CLI/MyNumberNET_CLI.csproj
+++ b/MyNumberNET_CLI/MyNumberNET_CLI.csproj
@@ -17,7 +17,7 @@
     <LangVersion>latest</LangVersion>
   </PropertyGroup>
   <ItemGroup>
-    <PackageReference Include="NLog" Version="5.2.0" />
+    <PackageReference Include="NLog" Version="6.0.4" />
     <PackageReference Include="System.Console" Version="4.3.1" />
     <PackageReference Include="System.Net.Sockets" Version="4.3.0" />
   </ItemGroup>
diff --git a/MyNumberNET_Test/MyNumberNET_Test.csproj b/MyNumberNET_Test/MyNumberNET_Test.csproj
index 066552b..a02ca83 100644
--- a/MyNumberNET_Test/MyNumberNET_Test.csproj
+++ b/MyNumberNET_Test/MyNumberNET_Test.csproj
@@ -17,10 +17,10 @@
     <LangVersion>latest</LangVersion>
   </PropertyGroup>
   <ItemGroup>
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.13.0" />
-    <PackageReference Include="MSTest.TestAdapter" Version="3.10.2" />
-    <PackageReference Include="MSTest.TestFramework" Version="3.10.2" />
-    <PackageReference Include="xunit" Version="2.4.2" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.14.1" />
+    <PackageReference Include="MSTest.TestAdapter" Version="3.10.4" />
+    <PackageReference Include="MSTest.TestFramework" Version="3.10.4" />
+    <PackageReference Include="xunit" Version="2.9.3" />
     <!-- Other test dependencies -->
   </ItemGroup>
   <ItemGroup>