Updating custom fields in Zoho Projects

I am wondering if anyone has experience with custom fields in Zoho Projects. I am struggling to update the field using either deluge or the api endpoint.

My code is:

//custom_Map = map();

custom_Map = {"UDF_DOUBLE_1":"0.27"};

update_Map = map();

update_Map.put("custom_fields",custom_Map.toList());

info update_Map;

// update_Task = zoho.projects.update("mcconaghyboats",project_ID,"tasks",task_ID,update_Map);

// Make the API call to update the project

resp = invokeurl

[

url: "https://projectsapi.zoho.com.cn/restapi/portal/mcconaghyboats/projects/" + project_ID + "/tasks/" + task_ID + "/"

type: POST

parameters: update_Map

connection: "zoho_projects"

];

info resp;

I have tried a number of different ways using both the internal connection and the api endpoint.

Does anyone have the correct syntax?

Thanks
Carl