My application sometime get 401 error on login via API

I’m currently developing a application on both iOS and Android, I holding back-end possition.
My kakaotalk login workflow is mobile will get accessToken then send it to back-end, then i will send it to as the document told me so.
It’s working sometime but mostly fail and response as 401 and Unauthorized message.
I really need some help cuz this is my first job
Thanks you


Tell me your app ID.
(My Application>App Settings>Summary > ID)