Comment 3 for bug 1619193

The same error string is widely used across endpoints and was re-used in register-name as a matter of consistency. Feel free to propose a string to globally enhance that message. Note there is also a similar message for missing agreement: https://bazaar.launchpad.net/~canonical-ca-hackers/software-center-agent/trunk/view/head:/src/devportal/api/handlers.py#L87