Insert unique value into JSON payload to make API request using serenity bdd and java

Question

I am really new to this, so maybe I am making an extremely simple mistake.

I have an automated test using Serenity and Java, making a POST request to an endpoint.

In the JSON payload there is a field "inspectionId" which requires a unique value. If the value already exists in the database, the POST fails and you get a 400.

I know how to generate the unique ID in the java code, but I cant figure out how to put it into the payload before sending the POST request.

I am trying to figure out how to insert the newly generated UUID into the payload before making the post request.

In my code I have the JSON file, a POJO class, and all of the methods. Mostly using Restassured,

I know there must be an easy way to insert the UUID into the payload before sending, but I cant wrap my head around how or when to do it. post request step

Here is the code in case it's necessary

@Then("Send a POST request to the mobile api {string} version {double} for {string}")
    public void sendAPOSTRequestToUploadPaperworkApi(String api, double apiVersionValue, String value) throws JsonProcessingException {
        Double apiVersion = apiVersionValue;
        String apiType = value;

              if (apiType.equals("startInspection"))
        {
            StartInspection startInspection = testData.get(threadName).getStartInspection(); //Gets the POJO file

            String endpoint = variables.getProperty("ct_api_endpoint") + api; //creates the route to the endpoint

            SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss"); //formats dates
            mapper.setDateFormat(simpleDateFormat);

            String body = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(startInspection); //sets the body object

            Response response = ControlTowerOperators.ctPostARequestWithBody(endpoint, body, apiVersion); 

            testData.get(threadName).setResponse(response);
        }
    }