input: from flask import Flask, request, json
  
  app = Flask(__name__)
  items = ["Apple", "Banana", "Orange"]
  
  def delete_item(item: str) -> str:
      """This function deletes a specified item from the list 'items'. If the item is found and successfully deleted, a success message is returned. If the item is not found, a failure message is returned.
      
      >>> delete_item("Apple")
      'Item successfully deleted.'
      >>> delete_item("Mango")
      'Item not found.'
      """
      if item in items:
          items.remove(item)
          return "Item successfully deleted."
      else:
          return "Item not found."
output:     if item in items:
          items.remove(item)
          return "Item successfully deleted."
      else:
          return "Item not found."