delete task error

//delete tasks error:
{"code":"INVALID_REQUEST","details":{},"message":"unable to process your request. please verify whether you have entered proper method name, parameter and parameter values.","status":"error"}

//search for recurring tasks and delete them
related_tasks = zoho.crm.getRelatedRecords("Tasks","Deals",deal_id);
delete_list = list();
for each  task in related_tasks
{
	recurring = task.getJSON("Recurring_Activity");
	if(!recurring.isNull())
	{
		task_id = task.get("id");
		delete_list.add("task_id");
	}
}
if(!delete_list.isEmpty())
{
	response = invokeurl
	[
		url :"https://www.zohoapis.com/crm/v3/Tasks?ids=" + delete_list
		type :DELETE
		connection:"crm_all"
	];
	info response;
}