Can you also confirm that the org you are testing with is on Okta Identity Engine? You can check which engine you are on by going to https://oktaDomain/.well-known/okta-organization : if you see "pipeline": "v1", you are using an Okta Classic Org that is not compatible with Interaction Code flow and if you see "pipeline" : "idx", you are using an Okta Identity Engine org.
This /interact endpoint is only invoked when useInteractionCodeFlow is enabled, so if you are on a classic org, set this to false.