How to create use HTTP service with fixed parameter


I am creating a service definition based on the external REST API (neo4j database).

The API requires to POST following parameter in BODY as an input:
{“query”: “…string query def”}

I have created a new service, created swagger to be able to use it from the console and everything works fine, if I post the above query in the console I gets proper response.

I need a service, that will always use the same query parameter and so I would like to avoid asking for the same query string again and again.

How can I do it? I tried to define it in parameter field in service definition but it does not propagate to the request.

Is there any way how to achieve this?

Many thanks