Using REST API to fetch data

Hello @rebecca009
Thank you for your question.

If the user is a logged-in user, you can find the data in ccc_my_favorite_post_ids in MySQL’s “wp_usermeta”.
If the user is not a logged-in user, the data is in the “localStorage” of the user’s browser.

This user meta ( ccc_my_favorite_post_ids ) is 'show_in_rest' => false, so it will not be shown in /wp-json/wp/v2/users.

Probably, you can add “wp_usermeta ( ccc_my_favorite_post_ids )” to the “WP_REST_API” of your theme.

Please refer to the following to try.

https://developer.www.ads-software.com/reference/functions/register_rest_field/
https://developer.www.ads-software.com/rest-api/extending-the-rest-api/modifying-responses/

or

https://developer.www.ads-software.com/reference/functions/register_rest_route/

Thanks