diff --git a/EnvelopeGenerator.Application/DependencyInjection.cs b/EnvelopeGenerator.Application/DependencyInjection.cs
index 2c33f529..23715f65 100644
--- a/EnvelopeGenerator.Application/DependencyInjection.cs
+++ b/EnvelopeGenerator.Application/DependencyInjection.cs
@@ -51,8 +51,8 @@ public static class DependencyInjection
         services.Configure<TotpSmsParams>(config.GetSection(nameof(TotpSmsParams)));
 
         services.AddHttpClientService<GtxMessagingParams>(config.GetSection(nameof(GtxMessagingParams)));
-        services.TryAddSingleton<ISmsSender, GTXSmsSender>();
-        services.TryAddSingleton<IEnvelopeSmsHandler, EnvelopeSmsHandler>();
+        services.TryAddScoped<ISmsSender, GTXSmsSender>();          // Changed: Singleton → Scoped
+        services.TryAddScoped<IEnvelopeSmsHandler, EnvelopeSmsHandler>(); // Changed: Singleton → Scoped
         services.TryAddSingleton<IAuthenticator, Authenticator>();
         services.TryAddSingleton<QRCodeGenerator>();
 
diff --git a/EnvelopeGenerator.Server/EnvelopeGenerator.Server.Client/EnvelopeGenerator.Server.Client.csproj b/EnvelopeGenerator.Server/EnvelopeGenerator.Server.Client/EnvelopeGenerator.Server.Client.csproj
index 66a2723d..50467b24 100644
--- a/EnvelopeGenerator.Server/EnvelopeGenerator.Server.Client/EnvelopeGenerator.Server.Client.csproj
+++ b/EnvelopeGenerator.Server/EnvelopeGenerator.Server.Client/EnvelopeGenerator.Server.Client.csproj
@@ -17,6 +17,7 @@
     <PackageReference Include="DevExpress.Blazor.Reporting.Viewer" Version="25.2.3" />
     <PackageReference Include="DevExpress.Drawing.Skia" Version="25.2.3" />
     <PackageReference Include="HarfBuzzSharp.NativeAssets.WebAssembly" Version="8.3.1.2" />
+    <PackageReference Include="Microsoft.Extensions.Http" Version="10.0.9" />
     <PackageReference Include="SkiaSharp.NativeAssets.WebAssembly" Version="3.119.1" />
     <PackageReference Include="SkiaSharp.Views.Blazor" Version="3.119.1" />
     <NativeFileReference Include="$(HarfBuzzSharpStaticLibraryPath)\2.0.23\*.a" />
diff --git a/EnvelopeGenerator.Server/EnvelopeGenerator.Server.Client/Services/AnnotationService.cs b/EnvelopeGenerator.Server/EnvelopeGenerator.Server.Client/Services/AnnotationService.cs
index 830b8206..693e4c6a 100644
--- a/EnvelopeGenerator.Server/EnvelopeGenerator.Server.Client/Services/AnnotationService.cs
+++ b/EnvelopeGenerator.Server/EnvelopeGenerator.Server.Client/Services/AnnotationService.cs
@@ -1,3 +1,4 @@
+using System.Net.Http;
 using System.Net.Http.Json;
 using System.Text.Json;
 using EnvelopeGenerator.Server.Client.Models;
@@ -15,13 +16,14 @@ namespace EnvelopeGenerator.Server.Client.Services;
 /// YARP route in <c>yarp.json</c> — no code change required.
 /// </summary>
 [Obsolete("Use SignatureService.")]
-public class AnnotationService(HttpClient http, IOptions<ApiOptions> apiOptions)
+public class AnnotationService(IHttpClientFactory httpClientFactory, IOptions<ApiOptions> apiOptions)
 {
     private static readonly JsonSerializerOptions _jsonOptions = new(JsonSerializerDefaults.Web);
 
     public async Task<IReadOnlyList<AnnotationDto>> GetAnnotationsAsync(string envelopeKey, CancellationToken cancel = default)
     {
-        var url = $"{apiOptions.Value.BaseUrl}/api/Annotation/{Uri.EscapeDataString(envelopeKey)}";
+        using var http = httpClientFactory.CreateClient("EnvelopeGenerator.Server");
+        var url = $"/api/Annotation/{Uri.EscapeDataString(envelopeKey)}";
         var response = await http.GetAsync(url, cancel);
 
         if (!response.IsSuccessStatusCode)
diff --git a/EnvelopeGenerator.Server/EnvelopeGenerator.Server.Client/Services/AuthService.cs b/EnvelopeGenerator.Server/EnvelopeGenerator.Server.Client/Services/AuthService.cs
index 562efcf8..ba23d283 100644
--- a/EnvelopeGenerator.Server/EnvelopeGenerator.Server.Client/Services/AuthService.cs
+++ b/EnvelopeGenerator.Server/EnvelopeGenerator.Server.Client/Services/AuthService.cs
@@ -1,4 +1,5 @@
 using System.Net;
+using System.Net.Http;
 using System.Net.Http.Json;
 using EnvelopeGenerator.Server.Client.Options;
 using Microsoft.Extensions.Options;
@@ -9,7 +10,7 @@ public enum EnvelopeLoginResult { Success, InvalidCode, NotFound, Error }
 
 public enum SenderLoginResult { Success, InvalidCredentials, Error }
 
-public class AuthService(HttpClient http, IOptions<ApiOptions> apiOptions)
+public class AuthService(IHttpClientFactory httpClientFactory, IOptions<ApiOptions> apiOptions)
 {
     private readonly ApiOptions _api = apiOptions.Value;
 
@@ -19,7 +20,8 @@ public class AuthService(HttpClient http, IOptions<ApiOptions> apiOptions)
     /// </summary>
     public async Task<bool> CheckEnvelopeAccessAsync(string envelopeKey, CancellationToken cancel = default)
     {
-        var response = await http.GetAsync($"{_api.BaseUrl}/api/auth/check/envelope/{Uri.EscapeDataString(envelopeKey)}", cancel);
+        using var http = httpClientFactory.CreateClient("EnvelopeGenerator.Server");
+        var response = await http.GetAsync($"/api/auth/check/envelope/{Uri.EscapeDataString(envelopeKey)}", cancel);
         return response.StatusCode == HttpStatusCode.OK;
     }
 
@@ -30,11 +32,12 @@ public class AuthService(HttpClient http, IOptions<ApiOptions> apiOptions)
     /// </summary>
     public async Task<EnvelopeLoginResult> LoginEnvelopeReceiverAsync(string envelopeKey, string accessCode, CancellationToken cancel = default)
     {
+        using var http = httpClientFactory.CreateClient("EnvelopeGenerator.Server");
         var form = new MultipartFormDataContent();
         form.Add(new StringContent(accessCode), "AccessCode");
 
         var response = await http.PostAsync(
-            $"{_api.BaseUrl}/api/Auth/envelope-receiver/{Uri.EscapeDataString(envelopeKey)}",
+            $"/api/Auth/envelope-receiver/{Uri.EscapeDataString(envelopeKey)}",
             form, cancel);
 
         return response.StatusCode switch
@@ -52,8 +55,9 @@ public class AuthService(HttpClient http, IOptions<ApiOptions> apiOptions)
     /// </summary>
     public async Task<bool> LogoutEnvelopeReceiverAsync(string envelopeKey, CancellationToken cancel = default)
     {
+        using var http = httpClientFactory.CreateClient("EnvelopeGenerator.Server");
         var response = await http.PostAsync(
-            $"{_api.BaseUrl}/api/auth/logout/envelope/{Uri.EscapeDataString(envelopeKey)}",
+            $"/api/auth/logout/envelope/{Uri.EscapeDataString(envelopeKey)}",
             null, cancel);
         return response.IsSuccessStatusCode;
     }
@@ -65,10 +69,11 @@ public class AuthService(HttpClient http, IOptions<ApiOptions> apiOptions)
     /// </summary>
     public async Task<SenderLoginResult> LoginSenderAsync(string username, string password, CancellationToken cancel = default)
     {
+        using var http = httpClientFactory.CreateClient("EnvelopeGenerator.Server");
         var requestBody = new { username, password };
 
         var response = await http.PostAsJsonAsync(
-            $"{_api.BaseUrl}/api/auth?cookie=true",
+            $"/api/auth?cookie=true",
             requestBody, cancel);
 
         return response.StatusCode switch
diff --git a/EnvelopeGenerator.Server/EnvelopeGenerator.Server.Client/Services/DocumentService.cs b/EnvelopeGenerator.Server/EnvelopeGenerator.Server.Client/Services/DocumentService.cs
index 9a39c719..f552033f 100644
--- a/EnvelopeGenerator.Server/EnvelopeGenerator.Server.Client/Services/DocumentService.cs
+++ b/EnvelopeGenerator.Server/EnvelopeGenerator.Server.Client/Services/DocumentService.cs
@@ -5,7 +5,7 @@ using EnvelopeGenerator.Server.Client.Options;
 
 namespace EnvelopeGenerator.Server.Client.Services;
 
-public class DocumentService(HttpClient http, IOptions<ApiOptions> apiOptions)
+public class DocumentService(IHttpClientFactory httpClientFactory, IOptions<ApiOptions> apiOptions)
 {
     private readonly ApiOptions _api = apiOptions.Value;
 
@@ -16,7 +16,8 @@ public class DocumentService(HttpClient http, IOptions<ApiOptions> apiOptions)
     /// <exception cref="HttpRequestException">Thrown when the API request fails.</exception>
     public async Task<byte[]?> GetDocumentAsync(string envelopeKey, CancellationToken cancel = default)
     {
-        var response = await http.GetAsync($"{_api.BaseUrl}/api/Document/{Uri.EscapeDataString(envelopeKey)}", cancel);
+        using var http = httpClientFactory.CreateClient("EnvelopeGenerator.Server");
+        var response = await http.GetAsync($"/api/Document/{Uri.EscapeDataString(envelopeKey)}", cancel);
 
         if (!response.IsSuccessStatusCode)
         {
diff --git a/EnvelopeGenerator.Server/EnvelopeGenerator.Server.Client/Services/EnvelopeReceiverService.cs b/EnvelopeGenerator.Server/EnvelopeGenerator.Server.Client/Services/EnvelopeReceiverService.cs
index 6383a4c5..852fb877 100644
--- a/EnvelopeGenerator.Server/EnvelopeGenerator.Server.Client/Services/EnvelopeReceiverService.cs
+++ b/EnvelopeGenerator.Server/EnvelopeGenerator.Server.Client/Services/EnvelopeReceiverService.cs
@@ -1,4 +1,5 @@
 using System.Net;
+using System.Net.Http;
 using System.Net.Http.Json;
 using System.Text.Json;
 using EnvelopeGenerator.Server.Client.Models;
@@ -11,7 +12,7 @@ namespace EnvelopeGenerator.Server.Client.Services;
 /// Retrieves the <see cref="EnvelopeReceiverDto"/> for the authenticated receiver
 /// from <c>GET api/EnvelopeReceiver/{envelopeKey}</c>.
 /// </summary>
-public class EnvelopeReceiverService(HttpClient http, IOptions<ApiOptions> apiOptions)
+public class EnvelopeReceiverService(IHttpClientFactory httpClientFactory, IOptions<ApiOptions> apiOptions)
 {
     private static readonly JsonSerializerOptions _jsonOptions = new(JsonSerializerDefaults.Web);
 
@@ -22,7 +23,8 @@ public class EnvelopeReceiverService(HttpClient http, IOptions<ApiOptions> apiOp
     /// <exception cref="HttpRequestException">Thrown when the API request fails.</exception>
     public async Task<EnvelopeReceiverDto?> GetAsync(string envelopeKey, CancellationToken cancel = default)
     {
-        var url = $"{apiOptions.Value.BaseUrl}/api/EnvelopeReceiver/{Uri.EscapeDataString(envelopeKey)}";
+        using var http = httpClientFactory.CreateClient("EnvelopeGenerator.Server");
+        var url = $"/api/EnvelopeReceiver/{Uri.EscapeDataString(envelopeKey)}";
         var response = await http.GetAsync(url, cancel);
 
         if (!response.IsSuccessStatusCode)
diff --git a/EnvelopeGenerator.Server/EnvelopeGenerator.Server.Client/Services/SignatureCacheService.cs b/EnvelopeGenerator.Server/EnvelopeGenerator.Server.Client/Services/SignatureCacheService.cs
index 98f1284a..6243f3ef 100644
--- a/EnvelopeGenerator.Server/EnvelopeGenerator.Server.Client/Services/SignatureCacheService.cs
+++ b/EnvelopeGenerator.Server/EnvelopeGenerator.Server.Client/Services/SignatureCacheService.cs
@@ -1,3 +1,4 @@
+using System.Net.Http;
 using System.Net.Http.Json;
 using Microsoft.Extensions.Options;
 using EnvelopeGenerator.Server.Client.Options;
@@ -8,7 +9,7 @@ namespace EnvelopeGenerator.Server.Client.Services;
 /// <summary>
 /// Client service for managing cached signatures via API.
 /// </summary>
-public class SignatureCacheService(HttpClient http, IOptions<ApiOptions> apiOptions)
+public class SignatureCacheService(IHttpClientFactory httpClientFactory, IOptions<ApiOptions> apiOptions)
 {
     private readonly ApiOptions _api = apiOptions.Value;
 
@@ -17,8 +18,9 @@ public class SignatureCacheService(HttpClient http, IOptions<ApiOptions> apiOpti
         SignatureCaptureDto signature,
         CancellationToken cancel = default)
     {
+        using var http = httpClientFactory.CreateClient("EnvelopeGenerator.Server");
         var response = await http.PostAsJsonAsync(
-            $"{_api.BaseUrl}/api/Cache/SignatureCapture/{Uri.EscapeDataString(envelopeKey)}",
+            $"/api/Cache/SignatureCapture/{Uri.EscapeDataString(envelopeKey)}",
             signature,
             cancel);
 
@@ -33,8 +35,9 @@ public class SignatureCacheService(HttpClient http, IOptions<ApiOptions> apiOpti
         string envelopeKey,
         CancellationToken cancel = default)
     {
+        using var http = httpClientFactory.CreateClient("EnvelopeGenerator.Server");
         var response = await http.GetAsync(
-            $"{_api.BaseUrl}/api/Cache/SignatureCapture/{Uri.EscapeDataString(envelopeKey)}",
+            $"/api/Cache/SignatureCapture/{Uri.EscapeDataString(envelopeKey)}",
             cancel);
 
         if (response.StatusCode == System.Net.HttpStatusCode.NotFound)
@@ -53,8 +56,9 @@ public class SignatureCacheService(HttpClient http, IOptions<ApiOptions> apiOpti
         string envelopeKey,
         CancellationToken cancel = default)
     {
+        using var http = httpClientFactory.CreateClient("EnvelopeGenerator.Server");
         var response = await http.DeleteAsync(
-            $"{_api.BaseUrl}/api/Cache/SignatureCapture/{Uri.EscapeDataString(envelopeKey)}",
+            $"/api/Cache/SignatureCapture/{Uri.EscapeDataString(envelopeKey)}",
             cancel);
 
         if (!response.IsSuccessStatusCode)
diff --git a/EnvelopeGenerator.Server/EnvelopeGenerator.Server.Client/Services/SignatureService.cs b/EnvelopeGenerator.Server/EnvelopeGenerator.Server.Client/Services/SignatureService.cs
index b87fb157..9fd76a62 100644
--- a/EnvelopeGenerator.Server/EnvelopeGenerator.Server.Client/Services/SignatureService.cs
+++ b/EnvelopeGenerator.Server/EnvelopeGenerator.Server.Client/Services/SignatureService.cs
@@ -1,3 +1,4 @@
+using System.Net.Http;
 using System.Net.Http.Json;
 using System.Text.Json;
 using EnvelopeGenerator.Server.Client.Models;
@@ -6,13 +7,14 @@ using Microsoft.Extensions.Options;
 
 namespace EnvelopeGenerator.Server.Client.Services;
 
-public class SignatureService(HttpClient http, IOptions<ApiOptions> apiOptions)
+public class SignatureService(IHttpClientFactory httpClientFactory, IOptions<ApiOptions> apiOptions)
 {
     private static readonly JsonSerializerOptions _jsonOptions = new(JsonSerializerDefaults.Web);
 
     public async Task<IReadOnlyList<SignatureDto>> GetAsync(string envelopeKey, CancellationToken cancel = default)
     {
-        var url = $"{apiOptions.Value.BaseUrl}/api/Signature/{Uri.EscapeDataString(envelopeKey)}";
+        using var http = httpClientFactory.CreateClient("EnvelopeGenerator.Server");
+        var url = $"/api/Signature/{Uri.EscapeDataString(envelopeKey)}";
         var response = await http.GetAsync(url, cancel);
 
         if (!response.IsSuccessStatusCode)
diff --git a/EnvelopeGenerator.Server/EnvelopeGenerator.Server/Program.cs b/EnvelopeGenerator.Server/EnvelopeGenerator.Server/Program.cs
index 85eb17e9..96e7846f 100644
--- a/EnvelopeGenerator.Server/EnvelopeGenerator.Server/Program.cs
+++ b/EnvelopeGenerator.Server/EnvelopeGenerator.Server/Program.cs
@@ -53,6 +53,9 @@ try
     builder.Services.AddControllers();
     builder.Services.AddHttpClient();
 
+    // Named HttpClient for internal API calls (same domain, uses relative paths)
+    builder.Services.AddHttpClient("EnvelopeGenerator.Server");
+
     // CORS Policy
     var allowedOrigins = config.GetSection("AllowedOrigins").Get<string[]>() ??
         throw new InvalidOperationException("AllowedOrigins section is missing in the configuration.");
@@ -289,20 +292,6 @@ try
 
     // HttpClient for server-side components (e.g., MainLayout with FontLoader)
     builder.Services.AddHttpContextAccessor();
-    builder.Services.AddScoped<HttpClient>(sp =>
-    {
-        var httpContextAccessor = sp.GetRequiredService<IHttpContextAccessor>();
-        var request = httpContextAccessor.HttpContext?.Request;
-
-        var httpClient = sp.GetRequiredService<IHttpClientFactory>().CreateClient();
-
-        if (request != null)
-        {
-            httpClient.BaseAddress = new Uri($"{request.Scheme}://{request.Host}");
-        }
-
-        return httpClient;
-    });
 
     // Business Services (Server specific)
     builder.Services.AddScoped<DocumentService>();