function clearTemplateSheet() {

  const ss = SpreadsheetApp.getActiveSpreadsheet();
  const templateSheet = ss.getSheetByName(INVOICE_TEMPLATE_SHEET_NAME);
  // Clears existing data from the template.
  const rngClear = templateSheet.getRangeList(['B10:B11', 'F10', 'F12', 'F14']).getRanges()
  rngClear.forEach(function (cell) {
    cell.clearContent();
  });
  // This sample only accounts for six rows of data 'B18:G24'. You can extend or make dynamic as necessary.
  templateSheet.getRange(18, 2, 7, 6).clearContent();
}
Resets the template sheet by clearing out customer data.
You use this to prepare for the next iteration or to view blank
the template for design.

Called by createInvoiceForCustomer() or by the user via custom menu item.