I encountered the same issue and was able to fix it by updating my project.clj to use [metosin/muuntaja 0.6.8] instead of 0.6.7 (as instructed in the book).
It looks like that keyword-keys-object-mapper wasn’t a part of jsonista until its v0.3.5, which wasn’t a part of earlier muuntaja’s.
I cannot answer the rest of the issue, but it looks likely that the author hasn’t fully updated this section?