Step 1 — Open Apps Script

1. Open your Google Sheet
2. Click Extensions → Apps Script

Step 2 — Paste the script

Delete all existing code and paste:

function doPost(e) {
  try {
    var ss = SpreadsheetApp.getActiveSpreadsheet();
    var params = JSON.parse(e.postData.contents);
    var sheet = ss.getSheetByName(params.tab);
    if (!sheet) return respond({status:'error',message:'Tab not found: '+params.tab});
    if (params.action === 'replace') {
      var last = sheet.getLastRow();
      if (last > 1) sheet.deleteRows(2, last - 1);
      if (params.rows && params.rows.length > 0)
        sheet.getRange(2,1,params.rows.length,params.rows[0].length).setValues(params.rows);
    }
    return respond({status:'success',rowsWritten:params.rows?params.rows.length:0});
  } catch(err) { return respond({status:'error',message:err.message}); }
}
function doGet(e){ return respond({status:'ok'}); }
function respond(obj){
  return ContentService.createTextOutput(JSON.stringify(obj))
    .setMimeType(ContentService.MimeType.JSON);
}

Step 3 — Deploy

1. Click Deploy → New Deployment
2. Type: Web App
3. Execute as: Me | Access: Anyone
4. Click Deploy → Authorize → Copy URL

⚠️ Every code change needs a new deployment.