curl --request POST \
  --url https://api.leanrails.com/v1/invoice_items \
  --header 'Authorization: Basic <encoded-value>' \
  --header 'Content-Type: application/json' \
  --header 'Idempotency-Key: <idempotency-key>' \
  --data '
{
  "customer": "<string>",
  "amount": 123,
  "currency": "<string>",
  "invoice": "<string>",
  "description": "<string>"
}
'

{
  "id": "<string>",
  "object": "invoiceitem",
  "amount": 123,
  "currency": "<string>",
  "livemode": true,
  "created": 123,
  "invoice": "<string>",
  "customer": "<string>",
  "description": "<string>"
}