doug's and autozone ?

Actually just keep trying it, that's what happened to me. I was checking to see if they were available and would accept the code, they were but I didn't have my money saved up yet so when I got my money together I went to order and it said unavailable, tried again for several days and it finally worked. I think possibly they only keep a few sets in stock or something, not quite sure but I got mine for the 20% off and free shipping.