The target resource does not have a current representation that would be acceptable to the user agent, according to the proactive negotiation header fields received in the request<sup>[1](#ref-1)</sup>, and the server is unwilling to supply a default representation.
The server SHOULD generate a payload containing a list of available representation characteristics and corresponding resource identifiers from which the user or user agent can choose the one most appropriate. A user agent MAY automatically select the most appropriate choice from that list. However, this specification does not define any standard for such automatic selection, as described in [RFC7231 Section 6.4.1][3].
