This isn’t very helpful. Our “App” has been working for over 10 years and now getting the “The request token for this page is invalid. It may have already been used, or expired because it is too old.Please go back to the site or application that sent you here and try again; it was probably just a mistake” message.
So it appears Twitter is making changes. Fine. Didn’t know that was happening but now I do. Have to apply for a new account on developer.twitter.com. Go through the process and this is the result:
No reason why there’s an error. No indication of what to do now. Not particularly helpful 
