solution

[massimilianoregis]

The problem is only around the item's value.

change the numeric value in real number and everything will work
"itemList": {
"item": [
{
"taxRate": 8.5000,
"name": "Curtains",
"description": "Blue curtains",
"unitPrice": 29.99,
"taxName": "Tax",
"quantity": 1
}
]
}