curl --request GET \
  --url https://api.{your-broker}.slate-labs.com/transfers/preview

{
  "from_login": "<string>",
  "to_login": "<string>",
  "amount": 123,
  "from_currency": "<string>",
  "to_currency": "<string>",
  "mid_rate": 123,
  "spread_pct": 123,
  "effective_rate": 123,
  "converted_amount": 123,
  "max_transferable": 123
}