Never used the api on this instance after the migration.
I did change the redirect URI at the client page to reflect my domain instead of the farmier domain.
You do need to have keys set up in order to use OAuth. Since you are coming off of Farmier, you will need to set those up. The farmOS API module will attempt to auto-generate them when it is first installed, but you are not installing it for the first time, so you will need to set them up manually.