Causa
content.format no es markdown ni html.
Qué hacer
Use markdown o html.
application/problem+json
{
"type": "https://masnet.com/developers/errors/invalid_content_format",
"title": "Formato de contenido no válido",
"status": 422,
"detail": "...",
"code": "invalid_content_format",
"correlation_id": "..."
}