When tried to update my apps a box pops up saying "this discounted price is only available to customers who own a previous version of this item."

I've been trying to update my apps on my iPhone however when i do a box pops up saying "this discounted price is only available to customers who own a previous version of this item. To purchase this item at full price, click buy." None of he apps i own cost me anything to download and when i do press buy the box will continuously appear and disappear.

​[Re-Titled by Moderator]