Rest Service Call using httpWrite function

Hi, 

I am trying to call Rest Service, post method using httpWrite function. I am able to get call end point, using smart service but it doesn't work with httpWrite function.

This service returns JSON response which i am supposed to capture.

Any pointers will be great help.

Code:-

load(
local!count: bind(
get: null,
set: a!httpWrite(
url: "XX.XX.XX:9090/.../getUnpaidFoodInvoicesByUnit",
method: "POST",
headers: {},
body: _
)
),
a!formLayout(
firstColumnContents: {
a!textField(
label: "request",
value: local!count,
readOnly: true
),
a!buttonLayout(
secondaryButtons: {
a!buttonWidget(
label: "start",
value: a!toJson(
{
"clientId": "FRA501",
"invoiceType": "Food"
}
),
saveInto: {
local!count
}
)
}
)
}
)
)