Manning doesn't pay that much to first time authors, and it looks like it's the first book for the author, Garrison Hinson-Hasty.
My guess is it's about $2k upfront and the author owes it back if they don't deliver.
Teiva Harsanyi did a good writeup recently about working with Manning as a first-time author. He got $2k upfront and $2k after delivering the first 1/3rd.[0]
When I wrote Elm in Action for Manning, I talked with them explicitly about the language being pre-1.0 and what would happen if there were breaking changes. The short answer was that it was something they dealt with all the time; if there were small changes, we could issue errata online, and if there were sufficiently large changes, we could do a second edition.
I did get an advance but I don't remember a clause about having to return any of it if I didn't earn it out. (I did earn it out, but I don't remember any expectation that I'd have to give them money back if I hadn't.) Also my memory was that it was more than $2k but it was about 10 years ago so I might be misremembering!
My guess is it's about $2k upfront and the author owes it back if they don't deliver.
Teiva Harsanyi did a good writeup recently about working with Manning as a first-time author. He got $2k upfront and $2k after delivering the first 1/3rd.[0]
[0] https://www.thecoder.cafe/p/100-go-mistakes