OAuth2.0 400 Error "Mismatch redirect uri"

I am attempting to authenticate the Bullhorn.com API using OAuth2 and I am getting the following error message:
“An error occurred during authorization: Access token URL returned a 400 when making a request for the access token. More data here: b’{\n “error” : “invalid_grant”,\n “error_description” : “Mismatch redirect uri.”\n}'”

I am setting the redirect URI parameter to https://parabola.io/api/steps/generic_api/callback for both the auth and access requests. I’ve attached screenshots of my current settings and parameters. Would appreciate any help with troubleshooting!

Here are the Bullhorn API Docs: Bullhorn REST API