fix this $[$the error $($if there is any$)]$ and add the messing things according to this:

In a shop, the purchasing procedure is as follows: the customer enters the shop, browses the items, asking for information or trying them out. If there are enough items in stock, they pick them up$,$ go to the checkout and pay for their purchases using any means of payment: cash, bank card or cheque. They may receive a discount on their purchases.

Question: Give the sequence diagram for the "pay for items at cash desk" use case.