I had a link with a form to complete linked to my facebook and it is no longer working ?

Which form have you added to your Facebook? I have checked the link you provided and form with ID 684336108254110 does not exist. 

Can you please try to remove form that you have added and add it again to your Facebook page. 

https://www.jotform.com/help/22-Adding-a-form-to-your-Facebook-page 

Hope this will help. Let us know if you need further assistance.