curl --request PATCH \
  --url https://api.hips.com/v2/payments/z68uoH7QZ1fizWZ3iPR6vbYE/refund \
  --header 'Accept: application/json' \
  --header 'Authorization: private_BQokikJOvBiI2HlWgH4olfQ2' \
  --header 'Content-Type: application/json \
  --data '{
    "amount": 1000,
    "items": [
       {  
          "name": "T-shirt out of stock, sorry.",
          "quantity": 1,
          "vat_amount": -250,
          "unit_price": -1000
       } 
   ]
  }'