Recently we realized our automated process to pull contacts, companies, and deals was no longer getting extracts, apparently we were no longer able to generate an access token from our refresh token. The last successful pull was 2018-01-04. I believe this is due to the implementation of oauth2 and deprecation of the old OAuth v1. In testing what I believe should be a valid request I get a '400' 'Bad Request' errror. Here are the connection parameters:
Header: 'Content-Type': 'application/x-www-form-urlencoded;charset=utf-8'
HTTPS Post to api.hubapi.com/oauth/v1/token
Also it would seem I can no longer access the app that I created years ago for the api.