REST API : List transactions for a subscription - help

[bekingo]

I am trying to use REST API : List transactions for a subscription  via postman...

https://api.sandbox.paypal.com/v1/billing/subscriptions/S-0001/transactions?start_time=2019-06-01T00...

so when Sending it out , I got invalid Request error see. the msg below :

why? what should be the format? some idea?

Subscription ID is in my btn...

API RESPONSE :

{
"name": "INVALID_REQUEST",
"message": "Request is not well-formed, syntactically incorrect, or violates schema.",
"debug_id": "da4a0b5478b6b",
"details": [
{
"value": "S-0001",
"location": "query",
"issue": "INVALID_PARAMETER_SYNTAX",
"description": "The value of a field does not conform to the expected format."
}
],
"links": [
{
"href": "https://developer.paypal.com/webapps/developer/docs/api/#VALIDATION_ERROR",
"rel": "information_link",
"method": "GET"
}
]
}