That fix was merged last year, though, so probably not exactly the same issue. But maybe related.
Just to be sure: did you enable the farm_fieldkit module (for Field Kit connection) and the farm_api_default_consumer module (for raw API use)? These both depend on the simple_oauth_password_grant module, which adds the ability to use password grants.
See the link I posted above to @jgaehring’s update for more details on where things stand.