In order for OAuth2 integration to work, the OAuth2 should redirect to https://api.unified.to/oauth/code with below scopes Below scopes should be enabled via Lever for Sync2Hire application.
opportunities:read:admin
opportunities:write:admin
users:read:admin
postings:read:admin
postings:write:admin
feedback:read:admin
stages:read:admin
users:write:admin
files:read:admin
files:write:admin