@nemobis hiya, the v0 API has been deprecated. We didn't get a chance to announce it as it was one of the services we moved behind the firewall after the October incident. We did not bring it back since the backend for fatcat's API needs serious work which is still ongoing.
Most important to note though is that we are making fatcat read-only as we did not have the resources to properly accept community contributions :( so even as v1 reaches parity with v0, the editing features will not return.