Can only use 2 gift cards at once online. This requires you to use your own money after that even if you have another one to cover the remaining balance.
I called CS and was told this is a recent update to the website.
I was not pleased with this and didn't allow them to brush me off.
After 35 minutes was able to get the small balance gift cards combined into 2. However, it is still in process and will take 3-5 business days before I can make the online purchase. I hope it works.