You have not defined a function called display_facebook_element, at least you did not include that in the code posted. Thus, you are getting the error. display_facebook_element isn’t a valid callback. It doesn’t exist.
You have not defined a function called display_facebook_element, at least you did not include that in the code posted. Thus, you are getting the error. display_facebook_element isn’t a valid callback. It doesn’t exist.