We have identified and believe to have addressed the issue which may have been causing 403 errors for the oauth/access_token requests. Affected timeframe is predicted from about 2021-9-30 19:30 UTC -2021-10-3-17:00 UTC.
Posted Oct 04, 2021 - 19:50 UTC
The Twitter data team is investigating a possible system irregularity currently affecting the OAuth1.0a flow step oauth/access_token responses. The presence and scope of any customer impact has not been determined at this time, but we will provide an update as soon as we know more.