Is it possible to get facebook PAGE access_token with USER access_token if the user is not the owner of the page, but has 'editor' role (for example)?
If yes, then how.
Here is described how to do that, but you must have ADMIN role.
I'm using Node.js
This is specifically addressed in the documentation.
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Your app will need to have the Admin role and permissions.
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As you're building your page-related app, you need the Admin permissions for a Page, contact a current Admin of that page and they can add you.
The answer is no. You can not access the Graph API or create content on behalf of a page without admin permissions.