openapi: 3.0.4
info:
  title: OpenAPI 3.0.4 body response text plain example
  version: 1
paths:
  /foo:
    post:
      requestBody:
        content:
          'text/plain':
            schema:
              type: string
        required: true
      responses:
        '200':
          description: OK
          content:
            text/plain:
              schema:
                type: string