// サムネにアイキャッチを使用
add_action( 'wp_head', 'add_meta_to_head' );
function add_meta_to_head() {
	echo '<meta name="thumbnail" content="' .wp_get_attachment_url( get_post_thumbnail_id() ). '" />';
}{"id":41,"count":23,"description":"","link":"https:\/\/riekoshimizu.com\/category\/illustration\/%e5%8c%bb%e7%99%82-%e8%82%8c%e6%a7%8b%e9%80%a0-%e5%81%a5%e5%ba%b7\/","name":"\u533b\u7642\/\u808c\u69cb\u9020\/\u5065\u5eb7","slug":"%e5%8c%bb%e7%99%82-%e8%82%8c%e6%a7%8b%e9%80%a0-%e5%81%a5%e5%ba%b7","taxonomy":"category","parent":37,"meta":[],"_links":{"self":[{"href":"https:\/\/riekoshimizu.com\/wp-json\/wp\/v2\/categories\/41"}],"collection":[{"href":"https:\/\/riekoshimizu.com\/wp-json\/wp\/v2\/categories"}],"about":[{"href":"https:\/\/riekoshimizu.com\/wp-json\/wp\/v2\/taxonomies\/category"}],"up":[{"embeddable":true,"href":"https:\/\/riekoshimizu.com\/wp-json\/wp\/v2\/categories\/37"}],"wp:post_type":[{"href":"https:\/\/riekoshimizu.com\/wp-json\/wp\/v2\/posts?categories=41"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}