PayPal Orders Create: Status 422, amount mismatch error despite matching values - paypal

Question

I am receiving a 422 UNPROCESSABLE_ENTITY error from paypal, indicating that my amount->value and breakdown values don't match up, but as far as I can tell they aren't. The request body is as follows:
"amount": {
"currency_code": "USD",
"value": 5,
"breakdown": {
"item_total": {
"value": 10,
"currency_code": "USD",
"discount": {
"value": 5,
"currency_code": "USD"
}
}
}
}
The error message says about amount->value: Should equal item_total + tax_total + shipping + handling + insurance - shipping_discount - discount.
Since I don't have shipping/handling/insurance/etc, shouldn't it just be 5(amount) = 10(item_total) - 5(discount)? What am I missing here?
Also, just in case it matters, I have just a single item in the purchase unit:
"items": [
{
"name": "...",
"unit_amount": {
"value": 10,
"currency_code": "USD"
},
"quantity": 1,
"category": "DIGITAL_GOODS"
}
]

Answer 1

discount is in the wrong place here:
"breakdown": {
"item_total": {
"value": 10,
"currency_code": "USD",
"discount": {
"value": 5,
"currency_code": "USD"
}
}
}
Move it out of item_total (where it's being ignored as an unknown field), and into the parent breakdown object where it belongs.

Answer 2

For PHP that would be :
$request->body = [
'intent' => 'CAPTURE',
'purchase_units' => [
[
'invoice_id' => 'some-id',
'amount' => [
'value' => 15,
'currency_code' => 'EUR',
'breakdown' => [
'shipping' => [
'value' => 5,
'currency_code' => 'EUR',
],
'item_total' => [
'value' => 10,
'currency_code' => 'EUR',
]
],
],
],
],
'application_context' => [
'cancel_url' => $cancelUrl,
'return_url' => $returnUrl,
],
];