WP Rest API V2 OR Operator in URL

First (since 4.7.1) you will need to re-activate the filter parameter.
Then make sure you have REST support activated for your custom post type (books).

Next you have to allowing the query args meta_query and parse it.

This answer shows how to do all this. Specifically, how to construct the meta query and the compare operators. : https://wordpress.stackexchange.com/a/227869/111022

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