diff --git a/qbosdk/apis/accounts.py b/qbosdk/apis/accounts.py
index 599da79..5c80814 100644
--- a/qbosdk/apis/accounts.py
+++ b/qbosdk/apis/accounts.py
@@ -25,7 +25,7 @@ def get_all_generator(self):
         """
         return self._query_get_all_generator('Account', Accounts.GET_ACCOUNTS)
 
-    def get_inactive(self, last_updated_time):
+    def get_inactive(self, last_updated_time: None):
         """
         Retrieves a list of inactive accounts from the QuickBooks Online API.
 
diff --git a/qbosdk/apis/customers.py b/qbosdk/apis/customers.py
index a28e4da..5e6d69c 100644
--- a/qbosdk/apis/customers.py
+++ b/qbosdk/apis/customers.py
@@ -34,7 +34,7 @@ def count(self):
         """
         return self._query(Customers.COUNT_CUSTOMERS)['totalCount']
 
-    def get_inactive(self, last_updated_time):
+    def get_inactive(self, last_updated_time: None):
         """
         Retrieves a list of inactive customers from the QuickBooks Online API.
 
diff --git a/qbosdk/apis/items.py b/qbosdk/apis/items.py
index 8d01899..01adc6b 100644
--- a/qbosdk/apis/items.py
+++ b/qbosdk/apis/items.py
@@ -26,7 +26,7 @@ def get_all_generator(self):
         """
         return self._query_get_all_generator('Item', Items.GET_ITEMS)
 
-    def get_inactive(self, last_updated_time):
+    def get_inactive(self, last_updated_time: None):
         """
         Retrieves a list of inactive items from the QuickBooks Online API.
 
diff --git a/qbosdk/apis/vendors.py b/qbosdk/apis/vendors.py
index a8705d2..04ced97 100644
--- a/qbosdk/apis/vendors.py
+++ b/qbosdk/apis/vendors.py
@@ -47,7 +47,7 @@ def search_vendor_by_display_name(self, display_name=None):
 
         return response['Vendor'][0] if 'Vendor' in response else None
 
-    def get_inactive(self, last_updated_time):
+    def get_inactive(self, last_updated_time: None):
         """
         Retrieves a list of inactive vendors from the QuickBooks Online API.