Well, you tell me 
I have no idea what you’re trying to do with the Function node tbh. I usually fetch Facebook page access tokens whenever needed like so:
So my regular long lived access token fetches the accounts I have access to. The Facebook API response includes a list of pages along with a short lived page-specific access token for each page:
I am then using this fresh token to perform whatever operation needs performing, in this example workflow posting to a page:
Works fine, even though I haven’t used this account for ages.