diff --git a/services/web/server/src/simcore_service_webserver/groups/_db.py b/services/web/server/src/simcore_service_webserver/groups/_db.py
index d2c6f4d2db5..e3ad2f824c7 100644
--- a/services/web/server/src/simcore_service_webserver/groups/_db.py
+++ b/services/web/server/src/simcore_service_webserver/groups/_db.py
@@ -7,6 +7,7 @@
 from models_library.groups import GroupAtDB
 from models_library.users import GroupID, UserID
 from pydantic import parse_obj_as
+from simcore_postgres_database.errors import UniqueViolation
 from simcore_postgres_database.utils_products import get_or_create_product_group
 from sqlalchemy import and_, literal_column
 from sqlalchemy.dialects.postgresql import insert
@@ -20,7 +21,11 @@
     convert_groups_db_to_schema,
     convert_groups_schema_to_db,
 )
-from .exceptions import GroupNotFoundError, UserInGroupNotFoundError
+from .exceptions import (
+    GroupNotFoundError,
+    UserAlreadyInGroupError,
+    UserInGroupNotFoundError,
+)
 
 _DEFAULT_PRODUCT_GROUP_ACCESS_RIGHTS = AccessRightsDict(
     read=False,
@@ -305,6 +310,7 @@ async def add_new_user_in_group(
     # first check if the group exists
     group: RowProxy = await _get_user_group(conn, user_id, gid)
     check_group_permissions(group, user_id, gid, "write")
+
     # now check the new user exists
     users_count = await conn.scalar(
         sa.select(sa.func.count()).where(users.c.id == new_user_id)
@@ -317,12 +323,18 @@ async def add_new_user_in_group(
     user_access_rights = _DEFAULT_GROUP_READ_ACCESS_RIGHTS
     if access_rights:
         user_access_rights.update(access_rights)
-    await conn.execute(
-        # pylint: disable=no-value-for-parameter
-        user_to_groups.insert().values(
-            uid=new_user_id, gid=group.gid, access_rights=user_access_rights
+
+    try:
+        await conn.execute(
+            # pylint: disable=no-value-for-parameter
+            user_to_groups.insert().values(
+                uid=new_user_id, gid=group.gid, access_rights=user_access_rights
+            )
         )
-    )
+    except UniqueViolation as exc:
+        raise UserAlreadyInGroupError(
+            uid=new_user_id, gid=gid, user_id=user_id, access_rights=access_rights
+        ) from exc
 
 
 async def _get_user_in_group_permissions(
diff --git a/services/web/server/src/simcore_service_webserver/groups/_handlers.py b/services/web/server/src/simcore_service_webserver/groups/_handlers.py
index 13d9acf71b5..1fa398e84f2 100644
--- a/services/web/server/src/simcore_service_webserver/groups/_handlers.py
+++ b/services/web/server/src/simcore_service_webserver/groups/_handlers.py
@@ -38,6 +38,7 @@
 from ._classifiers import GroupClassifierRepository, build_rrids_tree_view
 from .exceptions import (
     GroupNotFoundError,
+    UserAlreadyInGroupError,
     UserInGroupNotFoundError,
     UserInsufficientRightsError,
 )
@@ -67,6 +68,11 @@ async def wrapper(request: web.Request) -> web.StreamResponse:
         except UserInGroupNotFoundError as exc:
             raise web.HTTPNotFound(reason=f"User not found in group {exc.gid}") from exc
 
+        except UserAlreadyInGroupError as exc:
+            raise web.HTTPConflict(
+                reason=f"User is already in group {exc.gid}"
+            ) from exc
+
         except UserInsufficientRightsError as exc:
             raise web.HTTPForbidden from exc
 
diff --git a/services/web/server/src/simcore_service_webserver/groups/exceptions.py b/services/web/server/src/simcore_service_webserver/groups/exceptions.py
index 7556a8cae85..545c73a7727 100644
--- a/services/web/server/src/simcore_service_webserver/groups/exceptions.py
+++ b/services/web/server/src/simcore_service_webserver/groups/exceptions.py
@@ -4,19 +4,12 @@
 
 
 class GroupsError(WebServerBaseError):
-    msg_template = "{msg}"
-
-    def __init__(self, msg: str | None = None):
-        super().__init__(msg=msg or "Unexpected error occured in projects subpackage")
+    msg_template = "Groups plugin errored {msg}"
 
 
 class GroupNotFoundError(GroupsError):
     msg_template = "Group with id {gid} not found"
 
-    def __init__(self, gid, **extras):
-        super().__init__(**extras)
-        self.gid = gid
-
 
 class UserInsufficientRightsError(GroupsError):
     ...
@@ -25,7 +18,6 @@ class UserInsufficientRightsError(GroupsError):
 class UserInGroupNotFoundError(GroupsError):
     msg_template = "User id {uid} in Group {gid} not found"
 
-    def __init__(self, uid, gid, **extras):
-        super().__init__(**extras)
-        self.uid = uid
-        self.gid = gid
+
+class UserAlreadyInGroupError(GroupsError):
+    msg_template = "User `{uid}` is already in Group `{gid}`"