Expense application,how to start?

Sorry, I didn’t realize you were using a list and a data source. The blocks you had were actually probably correct.

Now you’re running into a known issue with the Get Value block. Namely that… it doesn’t work. See this: Google Sheets data source doesn't update every time - #6 by matt_conroy

I don’t have a good alternative for you but maybe Thunkable Staff can help with this.