Update app.py

app.py

@@ -35,6 +35,7 @@ WHATSAPP_PHONE_NUMBER_ID = os.getenv("WHATSAPP_PHONE_NUMBER_ID", "default_value"
 WHATSAPP_ACCESS_TOKEN = os.getenv("WHATSAPP_ACCESS_TOKEN", "default_value")
 MANAGEMENT_WHATSAPP_NUMBER = os.getenv("MANAGEMENT_WHATSAPP_NUMBER", "default_value")
 
+Base = declarative_base()
 
 class ChatHistory(Base):
     __tablename__ = "chat_history"