Excel Online (Business) actions work with an Excel table, not just cells that happen to look like a grid. List rows present in a table returns its value array. Add a row into a table appends one row. Update a row uses a key column and key value to find the record to change.
Choose a unique business key whenever the workbook contract supports one. A row number changes when people sort or insert rows, while an order reference can stay attached to the same order. The local connector exposes named tables so you can practice this distinction without uploading a workbook. It reports a missing table or missing key instead of silently creating a destination. Empty tables still have a valid array with zero rows. Preserve numeric-looking identifiers as text when their leading zeros matter.