diff --git a/lib/l10n/app_en.arb b/lib/l10n/app_en.arb
index 2d550c3..b5f9772 100644
--- a/lib/l10n/app_en.arb
+++ b/lib/l10n/app_en.arb
@@ -93,5 +93,7 @@
     "ipAddress": "IP address",
     "ipNotValid": "IP address not valid",
     "clientAddedSuccessfully": "Client added to the list successfully",
-    "addingClient": "Adding client..."
+    "addingClient": "Adding client...",
+    "clientNotAdded": "Client could not be added to the list",
+    "clientAnotherList": "This client is yet in another list"
 }
\ No newline at end of file
diff --git a/lib/l10n/app_es.arb b/lib/l10n/app_es.arb
index 3d7d6cc..c5cbb1c 100644
--- a/lib/l10n/app_es.arb
+++ b/lib/l10n/app_es.arb
@@ -93,5 +93,7 @@
     "ipAddress": "Dirección IP",
     "ipNotValid": "Dirección IP no válida",
     "clientAddedSuccessfully": "Cliente añadido a la lista satisfactoriamente",
-    "addingClient": "Añadiendo cliente..."
+    "addingClient": "Añadiendo cliente...",
+    "clientNotAdded": "El cliente no se pudo añadir a la lista",
+    "clientAnotherList": "El cliente ya está en otra lista"
 }
\ No newline at end of file
diff --git a/lib/screens/clients/blocked_allowed_list.dart b/lib/screens/clients/blocked_allowed_list.dart
index 23857bb..a933af4 100644
--- a/lib/screens/clients/blocked_allowed_list.dart
+++ b/lib/screens/clients/blocked_allowed_list.dart
@@ -59,6 +59,14 @@ class BlockedAllowedList extends StatelessWidget {
           )
         );
       }
+      else if (result['result'] == 'error' && result['message'] == 'client_another_list') {
+        ScaffoldMessenger.of(context).showSnackBar(
+          SnackBar(
+            content: Text(AppLocalizations.of(context)!.clientAnotherList),
+            backgroundColor: Colors.red,
+          )
+        );
+      }
       else {
         ScaffoldMessenger.of(context).showSnackBar(
           SnackBar(
diff --git a/lib/screens/clients/fab.dart b/lib/screens/clients/fab.dart
index e5b9d98..05412e1 100644
--- a/lib/screens/clients/fab.dart
+++ b/lib/screens/clients/fab.dart
@@ -62,10 +62,18 @@ class ClientsFab extends StatelessWidget {
           )
         );
       }
+      else if (result['result'] == 'error' && result['message'] == 'client_another_list') {
+        ScaffoldMessenger.of(context).showSnackBar(
+          SnackBar(
+            content: Text(AppLocalizations.of(context)!.clientAnotherList),
+            backgroundColor: Colors.red,
+          )
+        );
+      }
       else {
         ScaffoldMessenger.of(context).showSnackBar(
           SnackBar(
-            content: Text(AppLocalizations.of(context)!.clientNotRemoved),
+            content: Text(AppLocalizations.of(context)!.clientNotAdded),
             backgroundColor: Colors.red,
           )
         );
diff --git a/lib/services/http_requests.dart b/lib/services/http_requests.dart
index fe251be..87cb29a 100644
--- a/lib/services/http_requests.dart
+++ b/lib/services/http_requests.dart
@@ -285,6 +285,12 @@ Future requestAllowedBlockedClientsHosts(Server server, Map<String, List<String>
     if (result.statusCode == 200) {
       return {'result': 'success'};
     }
+    else if (result.statusCode == 400) {
+      return {
+        'result': 'error',
+        'message': 'client_another_list'
+      };
+    }
     else {
       return {'result': 'error'};
     }