including the ‘amp-next-page’ extension JavaScript

The plugin did not work for me, after setting up,when i tried it on https://validator.ampproject.org/ , it shows errors as shown this screenshot https://imgur.com/a/jyiMULN

one of the error is “”The tag ‘amp-next-page’ requires including the ‘amp-next-page’ extension JavaScript.
line 343, column 1″”

Please can anyone help advise me on what to do, in other to fix this?

The page I need help with: [log in to see the link]