How can I tell Stripe to calculate the tax for me during credit note creation via their API?

When using Stripe's automatic tax calculation (automatic_tax[enabled]=true) Stripe takes care of calculating the amount of tax that is applied to an invoice. The problem I'm running into is that when creating a "credit note" for a partial refund via Stripe's API, the refund_amount must equal the credit note amount (credit note amount = refund amount + tax), but I don't know what the calculated tax refund amount should be since Stripe handles that calculation on their end.

Consider the following code that will attempt to create a credit note on an invoice in the amount of $10.00:

$stripe->creditNotes->create([
  'invoice' => 'in_xxxxxxxxxxxxx',
  'refund_amount => 1000,
]);

The problem is that Stripe will calculate on their end that the refund_amount should be $10.70 (assuming 7% tax), and will return the following error:

> The sum of credit amount, refund amount and out of band amount ($10.00) must equal the credit note amount ($10.70).

So what I'm thinking I need is an additional parameter that tells Stripe that I'm expecting them to determine what the additional amount for tax should be; something like this:

$stripe->creditNotes->create([
  'invoice' => 'in_xxxxxxxxxxxxx',
  'refund_amount => 1000,
  'automatic_tax' => [
    'enabled' => true,
  ],
]);

But that parameter doesn't exist on the API. Does anyone have any suggestions on how to solve this problem?

Prior to creating your Credit Note you should retrieve the Invoice and look at either the total or the tax properties to know the assessed amount that you should use for your Credit Note.

The solution is to first create a "preview" credit note, which provides the calculated tax amounts. You can then add that tax onto the refund amount when creating the actual credit note:

// The amount to refund.
$amount = 1000; // ($10.00)

// First create a preview credit note.
$preview = $stripe->creditNotes->preview([
    'invoice' => 'in_xxxxxxxxxxxxx',
    'refund_amount' => $amount,
    'lines' => [
        [
            'type' => 'invoice_line_item',
            'invoice_line_item' => 'li_xxxxxxxxxxxxx',
            'amount' => $amount,
        ],
    ],
]);

// Collect the tax from the preview.
$tax = 0;
foreach ($preview->tax_amounts as $taxAmount) {
    $tax += $taxAmount->amount;
}

// Add the tax onto the refund amount.
$totalAmount = $amount + $tax;

// Issue the actual credit note.
$creditNote = $stripe->creditNotes->create([
    'invoice' => 'in_xxxxxxxxxxxxx',
    'refund_amount' => $totalAmount,
    'lines' => [
        [
            'type' => 'invoice_line_item',
            'invoice_line_item' => 'li_xxxxxxxxxxxxx',
            'amount' => $amount,
        ],
    ],
]);