Function getExistingDataFromSheet

getExistingDataFromSheet(
sheetName: string,
sheetId: string,
): Promise<Transaction[]>
Fetches existing data from a specified sheet in a Google Spreadsheet.
Parameters
- sheetName: string
  The name of the sheet to fetch data from (e.g., "expenses", "incomes").
- sheetId: string
  The Google Spreadsheet ID.
Returns Promise<Transaction[]>
A promise that resolves to an array of transactions.

Throws
Error If fetching data from the sheet fails.
- Defined in src/features/googleSheetService.ts:89