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- I have convert dueTime to UTC, dueTime contain date and time. But after task creation completed, I saw task's dueTime only contained date and ignored time in Ringcentral App.

- Then I click into edit task, I saw empty value in field time.

- But time in dueDate cannot apply

The Glip server takes the start and due date/time in UTC time zone. You have to convert your startDate and dueDate from local time to UTC time. For example, PST time zone is UTC-8. The date and time can be converted using JavaScript as follow:

var localTimeZoneOffset = 8*3600*1000
var sd = new Date("2020-12-02T12:00:00.000Z").getTime()
sd += localTimeZoneOffset
var dd = new Date("2020-12-06T13:00:00.000Z").getTime()
dd += localTimeZoneOffset
var startDate = new Date(sd).toISOString()
var dueDate = new Date(dd).toISOString()
//
var params = {
          subject: "Discuss new API",
          assignees: [ {id: "xxxxxx"}, {id: "xxxxxx"} ],
          completenessCondition: "Simple"
          startDate: startDate,
          dueDate: dueDate,
          color: "Red",
          section: "RnD",
          description: "Discuss with team of new API"
        }
var resp = await platform.post(endpoint, params)
var jsonObj = await resp.json()
console.log(jsonObj)

This should create the correct date and time.