This is the same as the earlier credit, just extended thru tomorrow to use. A qualifying book will have this on it's product page (near the top):
If that isn't there, about where the formats are listed, the credit won't work.
It isn't for "any Kindle edition", even if it does show up in your credits page (I already used mine, last month, so don't remember if it does).
Also, the OP in this thread included an affiliate tag, for those who want to be aware of those.