Does not access the OnResponse () method retrofit android

I am making a call from a post method that returns me an id generated through retrofit 2, however, in return, it never accesses the onResponse method, I already tried to use other objects and formats, but none worked. Below the service return:

 {  "_index": "smartfleet",  
    "_type": "op",   
    "_id": "AV2t5lWN2YWJ5ZApqt97",
    "_version": 1,
    "result": "created",
    "_shards": {
    "total": 3,
    "successful": 1,
    "failed": 0
},
    "created": true
}

Retrofit interface:

@POST("op")
Call<ResponseOperacao> enviaOperacao(@Body Operacao operacao);

public static final Retrofit retrofitGraficos = new Retrofit.Builder()
        .baseUrl("https://minha.url.aqui/v1/")
        .addConverterFactory(GsonConverterFactory.create())
        .build();