Bugs need fixing (.NET C# based Retail Software with SQL)

Requirements Requirement 1 Offer need looking Offers 1: Buy one get one free 2: Buy two get one free 3: Buy any 2/3/4 for fix amount 4: Mix and match offer (buy large bottle of coke and get coke free or buy box cigarette and get cigarette lighter for free) If you look at the screenshot current offer section it works 50% okay, I have created an offer for coke cans buy 3 coke cans for £1.50 original price for coke is 0.60 pence so three are for £1.80 I'm giving discount of 0.30 which means offer price is £1.50 when buying 3, customer will get 0.30 discount. If I scan or select 3 coke cans it applies discount fine but if you add the 4th can it reset price to original value it starts charging full amount. Requirement 2 Discount amount need to be printed on the receipt Requirement 3 If the product has already been discounted further discount need disabling Requirement 4 When giving discount from discount need checking that discount isn't been giving below the cost price if the cost price has been entered. Requirement 5 Payment screen need checking terms of code if it's doing what it supposed to do i.e. bringing proper values from the cart page. Requirement 6 VAT needs checking if it meets the HM Revenue requirements Requirement 7 Database needs checking if it needs cleaning up and if we can cut down the tables. Requirement 8 There is an Registry Key which makes software protected from being copied which is not working if you run it from bin folder but if you try to run the software from visual studio it just hangs up. Requirement 9 Full code need to be looking to find further bugs.