Hi Sean,
It looks like there’s an issue with the /User API call at the moment that isn’t setting the API key properly when the users are being created.
I’ll arrange to get a fix deployed, but in the meantime, to continue testing, could you re-generate the API key manually (see API Key Authentication) and I’ll be sure to notify you as soon as this is resolved.
Apologies for the inconvenience.
Regards
Phil