// 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":172,"count":10,"description":"","link":"https:\/\/riekoshimizu.com\/category\/illustration\/web%e3%82%b5%e3%82%a4%e3%83%88\/","name":"web\u30b5\u30a4\u30c8","slug":"web%e3%82%b5%e3%82%a4%e3%83%88","taxonomy":"category","parent":37,"meta":[],"_links":{"self":[{"href":"https:\/\/riekoshimizu.com\/wp-json\/wp\/v2\/categories\/172"}],"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=172"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}