I had the same "Authenticated user is not allowed access" error pop up. I read somewhere that once you have 10 domains registered with them the API works again. I already had 9 domains, so I thought what the heck! and I bought another one. Then, the API sharted working again shortly after. I am not happy about this and I don't trust them not to change things again in the long run. But, at least it lets me kick the can down the road until I have time to transfer to a different domain provider.