Ins and Outs of Giveaways

This year I am trying very hard to get better at marketing my books. I feel very lost most of the time.
Last year I tried a giveaway here on Goodreads for Dora's Story. It was a great promotion. I do hope the people who received the book enjoyed it.
Capri Capers is due out March 17. I planned a giveaway ahead of time, part of a pre-release campaign.
I busily formatted the novel and uploaded the ebook formats. They are up and in pre-release.
The print book is finally successfully uploaded. It has an ISBN number. I have ordered a proof copy.
Optimistically I tried to set up a giveaway for five copies. The ISBN didn't work. Why?
The comment said the book didn't exist. Well, it doesn't really yet. Except it does. It just isn't totally approved yet.
I have looked through other giveaways and some are for books due out shortly. Why does theirs list and mine not?
I don't know. I may eventually figure it out. In the meantime my giveaway is delayed. It will happen. Just not on my timeline.