Westpac One lets you export transactions for any date range as CSV. Depending on the account, the file's amount layout differs, which is exactly what trips up accounting imports. Here is the clean path from Westpac export to Xero, QuickBooks or OFX, processed entirely in your browser.
In Westpac One, open the account, choose the transaction view or search, set your date range, and export as CSV. Start with a short range on your first run so you can verify a handful of transactions against your statement before importing months of history.
Westpac exports commonly include Date, an Amount column (or, on some accounts, separate money in and money out columns), and narrative fields such as Other Party, Description, Reference and Particulars. Map Other Party to Payee and Description or Particulars to Description. If your file splits money in and out, assign those columns as Credit and Debit and the converter produces one correctly signed amount.
If every transaction imports as money in, the export almost certainly used unsigned in/out columns: set them under Credit and Debit rather than Amount and re-download.