The error message 'KeyError: key not found: "endpoint"' is displayed when importing a Swagger/OAS spec using the Red Hat 3scale toolbox

Issue

I have a Swagger/OpenAPI .json file that I wish to import. I am running the following command:

$ 3scale import openapi -d <INSTANCE> --staging-public-base-url=https://<STAGING URL> -t <SYSTEM NAME> /path/to/spec.json

All appears to be going well except at the end when an error is reported:

...
KeyError: key not found: "endpoint"
...