First you need:
- APP ID
- PAGE ID
- Create any page access token using the Graph API Explorer. This is called a short-lived token.
Step 1. Generate a long-lived access token
- Go to the Access Token Debugger
- Paste the short-lived token in the input text and debug it.
- Below you would find a 'Extend token' button. Press it and get the long-lived token.
Step 2. With the page_id and the long-lived access token you can generate a new acces token but this will be live forever running this URL from the graph explorer debugger identified as the associated Facebook App + the Page Access Token: PAGE_ID?fields=access_token&access_token=LONG_LIVED
Now you can debug it with the debugger tool and check that the token doesn't expire :D.
...and that's all :)