Formulas such as =ORVYN("orvyn/sgov-etf-price") read signed values with this key. Make one with the read scope only in the dashboard at orvyn.me: a leaked read key spends the calls you already bought and nothing more, and you can revoke it there.
The key is saved with this spreadsheet. Everyone the sheet is shared with can then spend its calls. To keep it to yourself, pass the key as the second argument from a cell instead.