PATCH participant attributes 412 Precondition Failed

  • Genesys Cloud v2 API
  • Node.js axios client
  • OAuth2 client credentials flow

Trying to understand why PATCH /api/v2/conversations/webchat/participants/{participantId}/attributes returns 412. payload is valid JSON per swagger but server rejects it instantly. no error body returned. just 412. code looks fine. am i missing a header or is this a known bug?