CloudTrail LookupEvent StartTime throwing SerializationException

Hi,

Im trying to use CloudTrail LookupEvent via Postman and per HTTP API it wants StartTime/EndTime as numerics (timestamp)
https://docs.aws.amazon.com/awscloudtrail/latest/APIReference/API_LookupEvents.html

But its throwing error :
{
"__type": "SerializationException"
}

Data Scenario:
URL - https://cloudtrail.us-east-1.amazonaws.com/
Region: us-east-1
ServiceName: cloudtrail
AWS accesskey and seckey : xxx xxx

Setup with additional http header:
x-amz-target = com.amazonaws.cloudtrail.v20131101.CloudTrail_20131101.LookupEvents
Content-Type = application/x-amz-json-1.1

Note: Using LookupEvents as x-amz-target return all result ignoring the json body request

using HTTP POST with JSON body as seen below:

{
"LookupAttributes": [
{
"AttributeKey": "EventSource",
"AttributeValue": "ec2.amazonaws.com"
}
],
"MaxResults": 5,
"StartTime" : 2021-05-18T01:03:34,
"EndTime" : 2021-05-19T01:03:34
}

Also i did tried the unix timestamp but its return an empty Events[], although using just StartTime return a data.

Appreciate if anyone from support team provide some insight.

Thanks