diff --git a/sinch/core/clients/sinch_client_async.py b/sinch/core/clients/sinch_client_async.py
index a32a223..aab97e5 100644
--- a/sinch/core/clients/sinch_client_async.py
+++ b/sinch/core/clients/sinch_client_async.py
@@ -1,3 +1,4 @@
+from logging import Logger
 from sinch.core.clients.sinch_client_base import ClientBase
 from sinch.core.clients.sinch_client_configuration import Configuration
 from sinch.core.token_manager import TokenManagerAsync
@@ -17,11 +18,11 @@ class ClientAsync(ClientBase):
     """
     def __init__(
         self,
-        key_id,
-        key_secret,
-        project_id,
-        logger_name=None,
-        logger=None,
+        key_id: str = None,
+        key_secret: str = None,
+        project_id: str = None,
+        logger_name: str = None,
+        logger: Logger = None,
         application_key: str = None,
         application_secret: str = None
     ):
diff --git a/sinch/core/clients/sinch_client_base.py b/sinch/core/clients/sinch_client_base.py
index 7f53fd0..45d6754 100644
--- a/sinch/core/clients/sinch_client_base.py
+++ b/sinch/core/clients/sinch_client_base.py
@@ -1,3 +1,4 @@
+from logging import Logger
 from abc import ABC, abstractmethod
 from sinch.core.clients.sinch_client_configuration import Configuration
 from sinch.domains.authentication import AuthenticationBase
@@ -21,15 +22,15 @@ class ClientBase(ABC):
     @abstractmethod
     def __init__(
         self,
-        key_id,
-        key_secret,
-        project_id,
-        logger_name=None,
-        logger=None,
+        key_id: str = None,
+        key_secret: str = None,
+        project_id: str = None,
+        logger_name: str = None,
+        logger: Logger = None,
         application_key: str = None,
         application_secret: str = None
     ):
         pass
 
     def __repr__(self):
-        return f"Sinch SDK client for project_id: {self.configuration.project_id}"
+        return "Sinch SDK client"
diff --git a/sinch/core/clients/sinch_client_configuration.py b/sinch/core/clients/sinch_client_configuration.py
index 74f0931..b087898 100644
--- a/sinch/core/clients/sinch_client_configuration.py
+++ b/sinch/core/clients/sinch_client_configuration.py
@@ -1,4 +1,5 @@
 import logging
+from logging import Logger
 from typing import Union
 
 from sinch.core.ports.http_transport import HTTPTransport
@@ -16,7 +17,7 @@ def __init__(
         project_id: str,
         transport: HTTPTransport,
         token_manager: Union[TokenManager, TokenManagerAsync],
-        logger=None,
+        logger: Logger = None,
         logger_name: str = None,
         disable_https=False,
         connection_timeout=10,
diff --git a/sinch/core/clients/sinch_client_sync.py b/sinch/core/clients/sinch_client_sync.py
index 0ec939c..5e81b78 100644
--- a/sinch/core/clients/sinch_client_sync.py
+++ b/sinch/core/clients/sinch_client_sync.py
@@ -1,3 +1,4 @@
+from logging import Logger
 from sinch.core.clients.sinch_client_base import ClientBase
 from sinch.core.clients.sinch_client_configuration import Configuration
 from sinch.core.token_manager import TokenManager
@@ -17,11 +18,11 @@ class Client(ClientBase):
     """
     def __init__(
         self,
-        key_id,
-        key_secret,
-        project_id,
-        logger_name=None,
-        logger=None,
+        key_id: str = None,
+        key_secret: str = None,
+        project_id: str = None,
+        logger_name: str = None,
+        logger: Logger = None,
         application_key: str = None,
         application_secret: str = None
     ):