In OpenAPI 3.0/Swagger, how can I refer to the selected server?

In my swagger.yml, I have the following:

openapi: 3.0.0
servers:
  - url: https://dev.myserver.com/v1
    description: dev
  - url: https://www.myserver.com/v1
    description: production  

And in one of the examples of my requestBody, I want to refer to the selected server. I tried something like this but it's giving an error that it's not able to reference to the selected server URL:

examples:
   TestExample:
      value:
         server:
            $ref: #/server/url   # This is giving an error that it's not able to reference the selected URL

In OpenAPI 3.0, how can I refer to the selected server?