OpenIntegrations/docs/en/examples/HTTPClient/SetHeaders.txt

    URL = FunctionParameters["HTTP_URL"];
    URL = URL + "/get";

    Headers = New Map;
    Headers.Insert("X-Header1", "Value1");
    Headers.Insert("X-Header2", "Value2");

    Result = OPI_HTTPRequests.NewRequest()
        .Initialize()
        .SetURL(URL)
        .SetHeaders(Headers) // <---
        .ProcessRequest("GET")
        .ReturnResponseAsJSONObject();