input: Write a python function to get the sales price of a product from a given ProductID using the requests module.
  assert get_sales_price('12345') == 299.99
  assert get_sales_price('67890') == 159.49
  assert get_sales_price('54321') == 89.99
output: def get_sales_price(product_id):
      import requests
      response = requests.get(f'https://api.example.com/products/{product_id}')
      if response.status_code == 200:
          product_info = response.json()
          return product_info.get('sales_price')
      else:
          return None