From the following description, describe the use cases, by identifying the actors, basic course of events and possible alternatives:

The PSL company has a website allowing online orders to buy Pizzas, Sandwiches, or Lasagna in the Lamar University campus. A customer can either walk-in at PSL to buy meals or he/she can make online orders using the PSL website. Either way, after selecting his/her choices and doing the payment, the PSL acknowledge order delivering the meals and the receipt.

Draw a sequence diagram realized from this use case description.