Calculating the discount amount with UK taxes

Retired Boards Appdev Customers Discounts And Orders
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1

Hello,

Could someone please help me understand how to calculate the effective discount amount for this particular line item (with UK VAT). The line item data is below:

{
  "id": 13976006394078,
  "current_quantity": 1,
  "fulfillable_quantity": 0,
  "fulfillment_status": "fulfilled",
  "gift_card": false,
  "price": "12.50",
  "price_set": {
    "shop_money": { "amount": "12.50", "currency_code": "GBP" },
    "presentment_money": { "amount": "12.50", "currency_code": "GBP" }
  },
  "product_exists": true,
  "properties": [],
  "quantity": 1,
  "requires_shipping": true,
  "taxable": true,
  "total_discount": "0.00",
  "total_discount_set": {
    "shop_money": { "amount": "0.00", "currency_code": "GBP" },
    "presentment_money": { "amount": "0.00", "currency_code": "GBP" }
  },
  "variant_inventory_management": "shopify",
  "tax_lines": [
    {
      "channel_liable": false,
      "price": "0.72",
      "price_set": {
        "shop_money": { "amount": "0.72", "currency_code": "GBP" },
        "presentment_money": { "amount": "0.72", "currency_code": "GBP" }
      },
      "rate": 0.2,
      "title": "GB VAT"
    }
  ],
  "duties": [],
  "discount_allocations": [
    {
      "amount": "8.19",
      "amount_set": {
        "shop_money": { "amount": "8.19", "currency_code": "GBP" },
        "presentment_money": { "amount": "8.19", "currency_code": "GBP" }
      },
      "discount_application_index": 0
    }
  ]
}

The discount applications is:

{
  "discount_applications": [
    {
      "target_type": "line_item",
      "type": "discount_code",
      "value": "20.0",
      "value_type": "fixed_amount",
      "allocation_method": "across",
      "target_selection": "all"
    }
  ]
}

Since the discount is “fixed_amount”, I assumed it should be based on the amount from the “discount_allocations” field, which is 8.19. However, in the Sales report that was generated, the discount amount is 6.82.

If we use a 20% tax rate for the 8.19 amount, it only equates to 6.55. Do you know the calculation that is needed to arrive at the 6.82 value?

Thanks!