diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9bef40e30..1c7c92595 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -13,12 +13,14 @@
 
 * [PostIt] Les avatars ne sont plus relies en string sur `Image.Source`: ils sont telecharges et lies en `Bitmap`.
 * [Yavsc.Api.Client] `ActivityApiClient` accepte une base d'avatar dediee et construit les URLs avatar depuis l'autorite d'identification.
+* [PostIt] Les clients Activites/Billing utilisent maintenant `ApiUrl` en lecture dynamique: un changement via Parametres prend effet sans redemarrer l'application (apres sauvegarde et rafraichissement de la page).
 * [PostIt] Le header de `MainPage` n'utilise plus `ScrollViewer`; remplacement par une barre de commandes basee sur `WrapPanel`.
 * [PostIt] Alignement de la navigation blogs: renommage `PushMainPageAsync` -> `PushBlogsPageAsync` et ajustement de `HomePageViewModel`.
 
 ### Fixed
 
-néant
+* [PostIt.Android] Correction d'un 404 sur la page Activites au premier lancement: la configuration embarquee pointait `ApiUrl` vers le host Blogs au lieu de l'API metier.
+* [PostIt] Correction du bouton Sauver de la page Parametres: binding vers `SaveCommand` pour persister correctement `ApiUrl`/`BlogsApiUrl`.
 
 ## [1.0.8-rc11] - unstable
 
diff --git a/src/PostIt/PostIt.Tests/ActivitiesPageViewModelTests.cs b/src/PostIt/PostIt.Tests/ActivitiesPageViewModelTests.cs
index 2e8d3e544..04cc0f314 100644
--- a/src/PostIt/PostIt.Tests/ActivitiesPageViewModelTests.cs
+++ b/src/PostIt/PostIt.Tests/ActivitiesPageViewModelTests.cs
@@ -39,6 +39,22 @@ public class ActivitiesPageViewModelTests
         Assert.Equal("https://business.example/api/v1/billing/Rdv", api.Paths[3]);
     }
 
+    [Fact]
+    public async Task ActivityApiClient_uses_updated_business_base_without_restart()
+    {
+        var api = new StubActivityApi();
+        var baseUrl = "https://business-a.example/api/v1/";
+        var client = new ActivityApiClient(api, () => baseUrl);
+
+        await client.GetCatalogAsync(ct: TestContext.Current.CancellationToken);
+
+        baseUrl = "https://business-b.example/api/v1/";
+        await client.GetUsersAsync("brush", TestContext.Current.CancellationToken);
+
+        Assert.Equal("https://business-a.example/api/v1/activity/catalog", api.Paths[0]);
+        Assert.Equal("https://business-b.example/api/v1/activity/brush/users", api.Paths[1]);
+    }
+
     [Fact]
     public async Task RefreshAsync_loads_first_activity_then_specialization_performers()
     {
diff --git a/src/PostIt/PostIt/Helpers/ServiceCollectionHelpers.cs b/src/PostIt/PostIt/Helpers/ServiceCollectionHelpers.cs
index f95f31e30..69f0a2dcd 100644
--- a/src/PostIt/PostIt/Helpers/ServiceCollectionHelpers.cs
+++ b/src/PostIt/PostIt/Helpers/ServiceCollectionHelpers.cs
@@ -26,9 +26,9 @@ public static class ServiceCollectionHelpers
         var userSearchClient = new UserSearchClient(api, settings.BlogsApiUrl);
         var activityClient = new ActivityApiClient(
             api,
-            settings.ApiUrl,
-            settings.Authentication?.Authority);
-        var billingClient = new BillingApiClient(api, settings.ApiUrl);
+            () => settings.ApiUrl,
+            () => settings.Authentication?.Authority);
+        var billingClient = new BillingApiClient(api, () => settings.ApiUrl);
         var userDirectory = new UserDirectory(userSearchClient);
 
         // Vues
diff --git a/src/PostIt/PostIt/Views/SettingsPage.axaml b/src/PostIt/PostIt/Views/SettingsPage.axaml
index 611b89954..bb19dfa3c 100644
--- a/src/PostIt/PostIt/Views/SettingsPage.axaml
+++ b/src/PostIt/PostIt/Views/SettingsPage.axaml
@@ -61,16 +61,11 @@
                     Click="ChooseAvatar_Click"
                     Margin="0,0,8,0"/>
 
-            <!-- Sauver: bound to the Save RelayCommand on the Settings
-                 VM. The source generator emits an ICommand property whose
-                 name matches the source method exactly (no "Command"
-                 suffix is added), so we bind {Binding Save} here. See
-                 AGENTS.md "Avalonia + CommunityToolkit.Mvvm : conventions
-                 de binding pour [RelayCommand]" for the full rationale.
-                 IsEnabled tracks IsDirty so the button auto-disables
-                 when there's nothing to persist. -->
+                <!-- Sauver: bind to the RelayCommand-generated property
+                 (SaveCommand). IsEnabled tracks IsDirty so the button
+                 auto-disables when there's nothing to persist. -->
             <Button Content="Sauver"
-                    Command="{Binding Save}"
+                    Command="{Binding SaveCommand}"
                     IsEnabled="{Binding IsDirty}"/>
                 </StackPanel>
         </StackPanel>
diff --git a/src/PostIt/PostIt/postit-settings sample.json b/src/PostIt/PostIt/postit-settings sample.json
index 6d8da8faf..e23839b1f 100644
--- a/src/PostIt/PostIt/postit-settings sample.json	
+++ b/src/PostIt/PostIt/postit-settings sample.json	
@@ -5,7 +5,7 @@
     },
     "RedirectUri": "postit://callback",
     "DarkMode": false,
-    "ApiUrl": "https://blogs.pschneider.fr/api/v1/",
+    "ApiUrl": "https://api.pschneider.fr/api/v1/",
     "Scopes": [
         "openid",
         "profile",
diff --git a/src/PostIt/PostIt/postit-settings.json b/src/PostIt/PostIt/postit-settings.json
index 079479515..080fed178 100644
--- a/src/PostIt/PostIt/postit-settings.json
+++ b/src/PostIt/PostIt/postit-settings.json
@@ -5,7 +5,7 @@
     },
     "RedirectUri": "postit://callback",
     "DarkMode": true,
-    "ApiUrl": "https://blogs.pschneider.fr/api/v1/",
+    "ApiUrl": "https://api.pschneider.fr/api/v1/",
     "Scopes": [
         "openid",
         "profile",
diff --git a/src/Yavsc.Api.Client/ActivityApiClient.cs b/src/Yavsc.Api.Client/ActivityApiClient.cs
index 52fad1a49..8199de9d4 100644
--- a/src/Yavsc.Api.Client/ActivityApiClient.cs
+++ b/src/Yavsc.Api.Client/ActivityApiClient.cs
@@ -19,19 +19,29 @@ public sealed class ActivityApiClient
     private const string PathPrefix = "activity";
 
     private readonly IYavscApiClient _api;
-    private readonly Uri _baseAddress;
-    private readonly Uri _avatarBaseAddress;
+    private readonly Func<string> _businessBaseAddress;
+    private readonly Func<string?> _avatarBaseAddress;
 
     public ActivityApiClient(IYavscApiClient api, string businessBaseAddress, string? avatarBaseAddress = null)
+        : this(
+            api,
+            () => businessBaseAddress,
+            () => avatarBaseAddress)
+    {
+    }
+
+    public ActivityApiClient(
+        IYavscApiClient api,
+        Func<string> businessBaseAddress,
+        Func<string?>? avatarBaseAddress = null)
     {
         _api = api ?? throw new ArgumentNullException(nameof(api));
-        if (string.IsNullOrEmpty(businessBaseAddress))
-            throw new ArgumentException("Base address is required.", nameof(businessBaseAddress));
+        _businessBaseAddress = businessBaseAddress ?? throw new ArgumentNullException(nameof(businessBaseAddress));
+        _avatarBaseAddress = avatarBaseAddress ?? (() => null);
 
-        _baseAddress = new Uri(businessBaseAddress, UriKind.Absolute);
-        _avatarBaseAddress = string.IsNullOrWhiteSpace(avatarBaseAddress)
-            ? _baseAddress
-            : new Uri(avatarBaseAddress, UriKind.Absolute);
+        // Validate initial values early to fail fast on invalid setup.
+        _ = ResolveBusinessBaseAddress();
+        _ = ResolveAvatarBaseAddress();
     }
 
     public Task<List<ActivityInfo>> GetCatalogAsync(
@@ -65,7 +75,7 @@ public sealed class ActivityApiClient
 
     public string BuildAvatarXsUrl(string? userName)
     {
-        var siteRoot = new Uri(_avatarBaseAddress, "/");
+        var siteRoot = new Uri(ResolveAvatarBaseAddress(), "/");
 
         if (string.IsNullOrWhiteSpace(userName))
         {
@@ -75,5 +85,22 @@ public sealed class ActivityApiClient
         return new Uri(siteRoot, $"avatars/{Uri.EscapeDataString(userName)}.xs.png").ToString();
     }
 
-    private string Absolute(string relativePath) => new Uri(_baseAddress, relativePath).ToString();
+    private string Absolute(string relativePath) => new Uri(ResolveBusinessBaseAddress(), relativePath).ToString();
+
+    private Uri ResolveBusinessBaseAddress()
+    {
+        var raw = _businessBaseAddress();
+        if (string.IsNullOrWhiteSpace(raw))
+            throw new InvalidOperationException("Business base address is required.");
+
+        return new Uri(raw, UriKind.Absolute);
+    }
+
+    private Uri ResolveAvatarBaseAddress()
+    {
+        var raw = _avatarBaseAddress();
+        return string.IsNullOrWhiteSpace(raw)
+            ? ResolveBusinessBaseAddress()
+            : new Uri(raw, UriKind.Absolute);
+    }
 }
diff --git a/src/Yavsc.Api.Client/BillingApiClient.cs b/src/Yavsc.Api.Client/BillingApiClient.cs
index 35a6722d5..c3a0be103 100644
--- a/src/Yavsc.Api.Client/BillingApiClient.cs
+++ b/src/Yavsc.Api.Client/BillingApiClient.cs
@@ -20,15 +20,20 @@ public sealed class BillingApiClient
     private const string PathPrefix = "billing";
 
     private readonly IYavscApiClient _api;
-    private readonly Uri _baseAddress;
+    private readonly Func<string> _businessBaseAddress;
 
     public BillingApiClient(IYavscApiClient api, string businessBaseAddress)
+        : this(api, () => businessBaseAddress)
+    {
+    }
+
+    public BillingApiClient(IYavscApiClient api, Func<string> businessBaseAddress)
     {
         _api = api ?? throw new ArgumentNullException(nameof(api));
-        if (string.IsNullOrWhiteSpace(businessBaseAddress))
-            throw new ArgumentException("Base address is required.", nameof(businessBaseAddress));
+        _businessBaseAddress = businessBaseAddress ?? throw new ArgumentNullException(nameof(businessBaseAddress));
 
-        _baseAddress = new Uri(businessBaseAddress, UriKind.Absolute);
+        // Validate initial value early to fail fast on invalid setup.
+        _ = ResolveBusinessBaseAddress();
     }
 
     public Task CreateAsync(string billingCode, object payload, CancellationToken ct = default)
@@ -121,7 +126,16 @@ public sealed class BillingApiClient
             ct: ct);
     }
 
-    private string Absolute(string relativePath) => new Uri(_baseAddress, relativePath).ToString();
+    private string Absolute(string relativePath) => new Uri(ResolveBusinessBaseAddress(), relativePath).ToString();
+
+    private Uri ResolveBusinessBaseAddress()
+    {
+        var raw = _businessBaseAddress();
+        if (string.IsNullOrWhiteSpace(raw))
+            throw new InvalidOperationException("Business base address is required.");
+
+        return new Uri(raw, UriKind.Absolute);
+    }
 
     private static BillingQueryDetailsDto MapRdv(RdvQueryResponse dto, string billingCode)
     {