I was about to buy all the DLCs for me and my two friends but unfortunately no 50% discount was applied for The Outcasts. See the screenshot.
Have you sent an email to BMT Micro ?
(as they handle the transactions etc.)
Why would I? I guess the author set wrong prices. BMT Micro is just a payment provider, they are not to determine the pricing of Cliff’s games, are they? 
This is why I report it here.
Well personally, I have found BMT Micro to be a very customer focused group and they would be able to provide an answer within 24 hours. And the answer might be to send an email to Cliff - but at least you will know for certain 
True, but if i am not mistaken, it is BMT website, there is the posibility that there could be an error in the coding that does not recognise the discount. Also it might be a case where the discount is applied on payment. Honestly i dont know, hence the suggestion to ask BMT Micro.
Never the less - I am glad you have decided to purchase the game straight from the developer.
May all your battles (and your friends) be Gratuitous