The spreadsheet requires access to Your Balance to use Smart Formulas
1. Start the extension via Extensions → Websheet AI → Start
2. Click on the Balance button in the sidebar
3. Activate the second checkbox in the Balance menu
Activate the checkbox "Allow access to Your Balance for Smart Formulas in this spreadsheet for both you and other editors," activate it, and click on Apply button
This will provide you, and other Spreadsheet editors access to Your Balance for the Smart Formulas. Other editors can also contribute their balances to the Spreadsheet calculations.