laportjo

Ok I found the solution. I put it in my theme functions file :

function add_votes_field() {
register_rest_field(
'idea', 
'votes', //Field Name in JSON RESPONSE
array(
        'get_callback'    => function() {
        return get_post_meta( get_the_ID(), 'votes', true );
        }
    )
);
}
add_action( 'rest_api_init', 'add_votes_field' );

function idea_push_update_custom_post_type( $args, $post_type ) {
    if ( $post_type !== 'idea' ) {
         return $args;
    }

    // Add additional IDEA CPT options.
    $idea_args = array(
        'show_in_rest' => true,
    );
 // Merge args together.
 return array_merge( $args, $idea_args );
}
add_filter( 'register_post_type_args', 'idea_push_update_custom_post_type', 10, 2 );