Is there a way to use the request query parameter value in the response

Question

I am trying to create a Mock API server using Postman. My request will have a query parameter key. I want to use the value passed to the key query parameter in the mock response.

Request: {{url}}/foo?key=3

Response:

{
   "3": {
      ...
   }
}

---

I tried {{url}}/foo?key={{key}}

{
    "{{key}}": {
        ...
    }
}

but that's just returning the {{key}} text as it is without any replacements. Is there any way I can use the query parameter values in the mock response?