Initial Application Setup

[MrDomoArigato]

I have a full stack app that I want to add authentication to.
The front end, back end, and authentik are all on different domains. So I'm using and OAuth2 Provider.
I have setup a provider and an application.

I currently have my front end running locally, so my application is setup to redirect to http://localhost. I have been testing my authentication by going to http://<authentik domain>/application/launch/<setup slug>/. I am prompted to login, but as soon as I enter my username I'm greeted with this error. I'm not real sure what to do.

Any help would be greatly appreciated.