diff --git a/pyoverkiz/exceptions.py b/pyoverkiz/exceptions.py
index a416f007..c260bdcf 100644
--- a/pyoverkiz/exceptions.py
+++ b/pyoverkiz/exceptions.py
@@ -128,6 +128,15 @@ class ApplicationNotAllowedError(ResourceAccessDeniedError):
     """Raised when the setup cannot be accessed through the application."""
 
 
+class NoOverkizUserError(ResourceAccessDeniedError):
+    """Raised when the account authenticated but has no Overkiz user on this server.
+
+    Login succeeds, but the token is not bound to an Overkiz user on this
+    endpoint. Seen for Somfy accounts that need the site-scoped multi-account
+    flow rather than the classic single-endpoint login.
+    """
+
+
 # Nexity
 class NexityBadCredentialsError(BadCredentialsError):
     """Raised when invalid credentials are provided to Nexity authentication API."""
diff --git a/pyoverkiz/response_handler.py b/pyoverkiz/response_handler.py
index ed2ded42..95b84ba9 100644
--- a/pyoverkiz/response_handler.py
+++ b/pyoverkiz/response_handler.py
@@ -21,6 +21,7 @@
     MaintenanceError,
     MissingAPIKeyError,
     MissingAuthorizationTokenError,
+    NoOverkizUserError,
     NoRegisteredEventListenerError,
     NoSuchActionGroupError,
     NoSuchDeviceError,
@@ -61,6 +62,7 @@
     ("AUTHENTICATION_ERROR", "API key is required", MissingAPIKeyError),
     ("AUTHENTICATION_ERROR", "No such user account", UnknownUserError),
     ("RESOURCE_ACCESS_DENIED", "Not authenticated", NotAuthenticatedError),
+    ("RESOURCE_ACCESS_DENIED", "No such user account", NoOverkizUserError),
     (
         "RESOURCE_ACCESS_DENIED",
         "Missing authorization token",
diff --git a/tests/fixtures/exceptions/cloud/no-overkiz-user.json b/tests/fixtures/exceptions/cloud/no-overkiz-user.json
new file mode 100644
index 00000000..9303d1e4
--- /dev/null
+++ b/tests/fixtures/exceptions/cloud/no-overkiz-user.json
@@ -0,0 +1,4 @@
+{
+    "errorCode": "RESOURCE_ACCESS_DENIED",
+    "error": "No such user account : user@example.tld"
+}
diff --git a/tests/test_client.py b/tests/test_client.py
index 0a818346..c556c0b2 100644
--- a/tests/test_client.py
+++ b/tests/test_client.py
@@ -630,6 +630,11 @@ async def test_get_diagnostic_data_returns_structured_dict(
                 exceptions.UnknownUserError,
                 400,
             ),
+            (
+                "cloud/no-overkiz-user.json",
+                exceptions.NoOverkizUserError,
+                403,
+            ),
             (
                 "cloud/no-such-command.json",
                 exceptions.InvalidCommandError,