I'm not sure if you've been able to get a never expiring token for the page, so I'll explain you the steps:
Open Graph API Explorer
Select your app from the drop-down
Click "Get Access Token" button, and select the
manage_pages
permission.Copy the token and run this in the browser:
https://graph.facebook.com/oauth/access_token?grant_type=fb_exchange_token&client_id={app-id}&client_secret={app-secret}&fb_exchange_token={step-3-token}
Copy the token from step-4 and paste in to the access_token field and call:
/{page-id}?fields=access_token
The token you get now is a never-expiring token, you can validate the same in Debugger .Use this in your app.
But beware, its not recommended to use this token on client side if your app is public.