diff --git a/mypy.ini b/mypy.ini
new file mode 100644
index 00000000..5a7abc0e
--- /dev/null
+++ b/mypy.ini
@@ -0,0 +1,5 @@
+[mypy]
+ignore_missing_imports = True
+strict_optional = True
+warn_redundant_casts = True
+warn_unused_ignores = True
diff --git a/src/app/api/dependencies.py b/src/app/api/dependencies.py
index 29e8b48b..915229ac 100644
--- a/src/app/api/dependencies.py
+++ b/src/app/api/dependencies.py
@@ -64,7 +64,7 @@ async def get_optional_user(
         if token_data is None:
             return None
 
-        return await get_current_user(token_value, is_deleted=False, db=db)
+        return await get_current_user(token_value, db=db)
     
     except HTTPException as http_exc:
         if http_exc.status_code != 401:
diff --git a/src/app/api/paginated.py b/src/app/api/paginated.py
index 803f46b2..10614121 100644
--- a/src/app/api/paginated.py
+++ b/src/app/api/paginated.py
@@ -1,4 +1,4 @@
-from typing import TypeVar, Generic, List
+from typing import TypeVar, Generic, List, Dict, Any
 
 from pydantic import BaseModel
 
@@ -19,7 +19,7 @@ def paginated_response(
         crud_data: ListResponse[SchemaType], 
         page: int, 
         items_per_page: int
-) -> PaginatedListResponse[SchemaType]:
+) -> Dict[str, Any]:
     """
     Create a paginated response based on the provided data and pagination parameters.
 
@@ -34,8 +34,8 @@ def paginated_response(
 
     Returns
     -------
-    PaginatedListResponse[SchemaType]
-        A structured paginated response containing the list of items, total count, pagination flags, and numbers.
+    Dict[str, Any]
+        A structured paginated response dict containing the list of items, total count, pagination flags, and numbers.
 
     Note
     ----
diff --git a/src/app/core/db/models.py b/src/app/core/db/models.py
index 8c6c8cf5..642ae548 100644
--- a/src/app/core/db/models.py
+++ b/src/app/core/db/models.py
@@ -1,9 +1,11 @@
 import uuid as uuid_pkg
 from datetime import datetime
 from sqlalchemy import Column, DateTime, Boolean, text
+from sqlalchemy.dialects.postgresql import UUID
 
 class UUIDMixin:
-    uuid: uuid_pkg.UUID = Column(uuid_pkg.UUID(as_uuid=True), primary_key=True, default=uuid_pkg.uuid4, server_default=text("gen_random_uuid()"))
+    uuid: uuid_pkg.UUID = Column(UUID, primary_key=True, default=uuid_pkg.uuid4, server_default=text("gen_random_uuid()"))
+
 
 class TimestampMixin:
     created_at: datetime = Column(DateTime, default=datetime.utcnow, server_default=text("current_timestamp(0)"))
diff --git a/src/app/core/exceptions/cache_exceptions.py b/src/app/core/exceptions/cache_exceptions.py
index a2b5864b..3a75d9c7 100644
--- a/src/app/core/exceptions/cache_exceptions.py
+++ b/src/app/core/exceptions/cache_exceptions.py
@@ -8,3 +8,9 @@ class InvalidRequestError(Exception):
     def __init__(self, message="Type of request not supported."):
         self.message = message
         super().__init__(self.message)
+
+
+class MissingClientError(Exception):
+    def __init__(self, message="Client is None."):
+        self.message = message
+        super().__init__(self.message)
diff --git a/src/app/core/exceptions/http_exceptions.py b/src/app/core/exceptions/http_exceptions.py
index 5c937429..65506a4c 100644
--- a/src/app/core/exceptions/http_exceptions.py
+++ b/src/app/core/exceptions/http_exceptions.py
@@ -1,9 +1,10 @@
+from http import HTTPStatus
 from fastapi import HTTPException, status
 
 class CustomException(HTTPException):
     def __init__(self, status_code: int = status.HTTP_500_INTERNAL_SERVER_ERROR, detail: str | None = None):
         if not detail:
-            detail = status_code.description
+            detail = HTTPStatus(status_code).description
         super().__init__(status_code=status_code, detail=detail)
 
 
diff --git a/src/app/core/schemas.py b/src/app/core/schemas.py
index d44e3b04..fd4d1036 100644
--- a/src/app/core/schemas.py
+++ b/src/app/core/schemas.py
@@ -18,23 +18,29 @@ class TimestampSchema(BaseModel):
     updated_at: datetime = Field(default=None)
 
     @field_serializer("created_at")
-    def serialize_dt(self, created_at: datetime | None, _info):
-        return created_at.isoformat()
+    def serialize_dt(self, created_at: datetime | None, _info) -> str | None:
+        if created_at is not None:
+            return created_at.isoformat()
+        
+        return None
 
     @field_serializer("updated_at")
-    def serialize_updated_at(self, updated_at: datetime | None, _info):
+    def serialize_updated_at(self, updated_at: datetime | None, _info) -> str | None:
         if updated_at is not None:
             return updated_at.isoformat()
 
+        return None
 
 class PersistentDeletion(BaseModel):
     deleted_at: datetime | None = Field(default=None)
     is_deleted: bool = False
 
     @field_serializer('deleted_at')
-    def serialize_dates(self, deleted_at: datetime | None, _info):
+    def serialize_dates(self, deleted_at: datetime | None, _info) -> str | None:
         if deleted_at is not None:
             return deleted_at.isoformat()
+        
+        return None
 
 
 # -------------- token --------------
diff --git a/src/app/core/utils/cache.py b/src/app/core/utils/cache.py
index ef3f4653..dbbcdfe1 100644
--- a/src/app/core/utils/cache.py
+++ b/src/app/core/utils/cache.py
@@ -1,4 +1,4 @@
-from typing import Callable, Union, List, Dict, Any
+from typing import Callable, Union, Tuple, List, Dict, Any
 import functools
 import json
 import re
@@ -7,12 +7,12 @@
 from fastapi.encoders import jsonable_encoder
 from redis.asyncio import Redis, ConnectionPool
 
-from app.core.exceptions.cache_exceptions import CacheIdentificationInferenceError, InvalidRequestError
+from app.core.exceptions.cache_exceptions import CacheIdentificationInferenceError, InvalidRequestError, MissingClientError
 
 pool: ConnectionPool | None = None
 client: Redis | None = None
 
-def _infer_resource_id(kwargs: Dict[str, Any], resource_id_type: Union[type, str]) -> Union[None, int, str]:
+def _infer_resource_id(kwargs: Dict[str, Any], resource_id_type: Union[type, Tuple[type, ...]]) -> Union[None, int, str]:
     """
     Infer the resource ID from a dictionary of keyword arguments.
 
@@ -20,8 +20,8 @@ def _infer_resource_id(kwargs: Dict[str, Any], resource_id_type: Union[type, str
     ----------
     kwargs: Dict[str, Any] 
         A dictionary of keyword arguments.
-    resource_id_type: Union[type, str] 
-        The expected type of the resource ID, which can be an integer (int) or a string (str).
+    resource_id_type: Union[type, Tuple[type, ...]]
+        The expected type of the resource ID, which can be integer (int) or a string (str).
         
     Returns
     -------
@@ -30,8 +30,8 @@ def _infer_resource_id(kwargs: Dict[str, Any], resource_id_type: Union[type, str
 
     Note
     ----
-        - When `resource_id_type` is 'int', the function looks for an argument with the key 'id'.
-        - When `resource_id_type` is 'str', it attempts to infer the resource ID as a string.
+        - When `resource_id_type` is `int`, the function looks for an argument with the key 'id'.
+        - When `resource_id_type` is `str`, it attempts to infer the resource ID as a string.
     """
     resource_id = None
     for arg_name, arg_value in kwargs.items():
@@ -177,7 +177,10 @@ async def _delete_keys_by_pattern(pattern: str):
     - Be cautious with patterns that could match a large number of keys, as deleting
       many keys simultaneously may impact the performance of the Redis server.
     """
-    cursor = "0"
+    if client is None:
+        raise MissingClientError
+
+    cursor = -1
     while cursor != 0:
         cursor, keys = await client.scan(cursor, match=pattern, count=100)
         if keys:
@@ -188,7 +191,7 @@ def cache(
         key_prefix: str, 
         resource_id_name: Any = None, 
         expiration: int = 3600, 
-        resource_id_type: Union[type, List[type]] = int,
+        resource_id_type: Union[type, Tuple[type, ...]] = int,
         to_invalidate_extra: Dict[str, Any] | None = None,
         pattern_to_invalidate_extra: List[str] | None = None
 ) -> Callable:
@@ -207,8 +210,8 @@ def cache(
         otherwise, the resource ID is inferred from the function's arguments.
     expiration: int, optional
         The expiration time for the cached data in seconds. Defaults to 3600 seconds (1 hour).
-    resource_id_type: Union[type, List[type]], optional
-        The expected type of the resource ID. This can be a single type (e.g., int) or a list of types (e.g., [int, str]). 
+    resource_id_type: Union[type, Tuple[type, ...]], default int
+        The expected type of the resource ID. This can be a single type (e.g., int) or a tuple of types (e.g., (int, str)). 
         Defaults to int. This is used only if resource_id_name is not provided.
     to_invalidate_extra: Dict[str, Any] | None, optional
         A dictionary where keys are cache key prefixes and values are templates for cache key suffixes. 
@@ -286,6 +289,9 @@ async def update_item(request: Request, item_id: int, data: dict, user_id: int):
     def wrapper(func: Callable) -> Callable:
         @functools.wraps(func)
         async def inner(request: Request, *args, **kwargs) -> Response:
+            if client is None:
+                raise MissingClientError
+
             if resource_id_name:
                 resource_id = kwargs[resource_id_name]
             else:
diff --git a/src/app/crud/crud_base.py b/src/app/crud/crud_base.py
index 197ab300..fab8fb33 100644
--- a/src/app/crud/crud_base.py
+++ b/src/app/crud/crud_base.py
@@ -13,8 +13,9 @@
     _auto_detect_join_condition,
     _add_column_with_prefix
 )
+from app.core.db.database import Base
 
-ModelType = TypeVar("ModelType")
+ModelType = TypeVar("ModelType", bound=Base)
 CreateSchemaType = TypeVar("CreateSchemaType", bound=BaseModel)
 UpdateSchemaType = TypeVar("UpdateSchemaType", bound=BaseModel)
 UpdateSchemaInternalType = TypeVar("UpdateSchemaInternalType", bound=BaseModel)
diff --git a/src/app/schemas/post.py b/src/app/schemas/post.py
index 0899f2d5..6b3e5379 100644
--- a/src/app/schemas/post.py
+++ b/src/app/schemas/post.py
@@ -66,7 +66,7 @@ class PostCreateInternal(PostCreate):
     created_by_user_id: int
 
 
-class PostUpdate(PostBase):
+class PostUpdate(BaseModel):
     model_config = ConfigDict(extra='forbid')
     
     title: Annotated[
diff --git a/src/app/schemas/user.py b/src/app/schemas/user.py
index 026c87b5..60cb6df3 100644
--- a/src/app/schemas/user.py
+++ b/src/app/schemas/user.py
@@ -32,7 +32,6 @@ class User(TimestampSchema, UserBase, UUIDSchema, PersistentDeletion):
 
 class UserRead(BaseModel):
     id: int
-    tier_id: int
     
     name: Annotated[
         str,