VPN-only provider: Webapp test fails with "errors":{"login":["needs to be a valid email address"]}}

I deployed a single-node VPN provider today and go this:

--- leap/workshop.bitmask.net » leap test                                                                                                        1 ↵
 = [blackbox] PASS: Network > Can connect to internet?
 = [blackbox] PASS: Network > Is stunnel running?
 = [blackbox] PASS: Network > Is shorewall running?
 = [blackbox] PASS: Network > Are server certificates valid?
 = [blackbox] PASS: CouchDB > Are daemons running?
 = [blackbox] PASS: CouchDB > Is CouchDB running?
 = [blackbox] PASS: CouchDB > Do ACL users exist?
 = [blackbox] PASS: CouchDB > Do required databases exist?
 = [blackbox] PASS: CouchDB > Can records be created?
 = [blackbox] PASS: OpenVPN > Are daemons running?
 = [blackbox] PASS: OpenVPN > Can connect to openvpn?
 = [blackbox] PASS: Webapp > Can contact couchdb?
 = [blackbox] PASS: Webapp > Are daemons running?
 = [blackbox] PASS: Webapp > Can access webapp?
 = [blackbox] FAIL: Webapp > Can create and authenticate and delete user via API? [webapp.rb:37]:
 = [blackbox]   Expected success code from POST https://api.DOMAIN:4430/1/users.json, but got 422 instead.
 = [blackbox]   {"errors":{"login":["needs to be a valid email address"]}}
 = [blackbox] Tests halted on failure (because of --no-continue).
 = bailing out

This is the node config:

--- leap/workshop.bitmask.net » cat nodes/blackbox.json
{
  "couch": {
    "mode": "plain"
  },
  "ip_address": "37.218.245.94",
  "openvpn": {
    "gateway_address": "37.218.245.4",
    "ports": [
      "443"
    ],
    "protocols": [
      "tcp"
    ]
  },
  "services": [
    "couchdb",
    "openvpn",
    "webapp"
  ]
}