// 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":178,"count":1,"description":"","link":"https:\/\/riekoshimizu.com\/category\/illustration\/%e2%98%85%e3%82%ab%e3%83%86%e3%82%b4%e3%83%aa%e3%83%bc%e5%88%a5\/line%e3%82%b9%e3%82%bf%e3%83%b3%e3%83%97%e3%80%81%e7%b5%b5%e6%96%87%e5%ad%97\/","name":"LINE\u30b9\u30bf\u30f3\u30d7\u3001\u7d75\u6587\u5b57","slug":"line%e3%82%b9%e3%82%bf%e3%83%b3%e3%83%97%e3%80%81%e7%b5%b5%e6%96%87%e5%ad%97","taxonomy":"category","parent":171,"meta":[],"_links":{"self":[{"href":"https:\/\/riekoshimizu.com\/wp-json\/wp\/v2\/categories\/178"}],"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\/171"}],"wp:post_type":[{"href":"https:\/\/riekoshimizu.com\/wp-json\/wp\/v2\/posts?categories=178"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}