Getting the sourceString of all pivot tables in a workbook

I'm trying to run through all pivottables in an Excel workbook and list their sources, but I'm not succeeding. I'm using code like this:

async function SearchInPivots(
  context, wb: Excel.Workbook) {
  let foundPivots = new foundCollection();
  let pts = wb.pivotTables.load("items");
  let ptCt = pts.getCount();
  await context.sync();
  let ptColl = [];
  let pt:Excel.PivotTable = null;
  for (let i: number = 0; i < ptCt.value; i++) {
    pt = pts[i].load("getDataSourceString");
    ptColl.push(pt);
  }
  await context.sync();

  for (let i: number = 0; i < ptColl.length; i++) {
    console.log(ptColl[i].getDataSourceString());
  }
  return foundPivots;
}

 What am I missing?

Cross-posted here: https://stackoverflow.com/questions/74178968/getting-the-sourcestring-of-all-pivot-tables-in-a-workbook