New to TrueBlue, made Amazon purchase and miles posted in about 30 days. I would suggest making sure you click through the Jet Blue site. Do not have Amazon windows open prior to your shopping trip. Other posters suggested the item not be in your shopping cart beforehand.

Not sure if this works, but if you have two browsers on your computer, you could try using one to browse Amazon and your items, while clicking through Jet Blue and making the Amazon purchase on the other browser.