json api invali format

I use json plugin api to create this api : http://infoplus.vn/api/get_category_index/?json_unescaped_unicode=1

But when I go to json structure http://jsonlint.com/ to check the received error messages Unexpected token < / em >

I checked the few characters that appear in the first empty line ..

Please do help me fix guide with
Thank you . !

https://ww.wp.xz.cn/plugins/json-api/