Google Ads Script – getConversionRate() method always return 0 value

I’m using google ads script to pull some data to sheet. my goal is to get conversion Rate for each campaign.

this is my code

   var campaignIterator = AdsApp.campaigns().get();
   while (campaignIterator.hasNext()) {
    var campaign = campaignIterator.next();
     const stats = campaign.getStatsFor('LAST_MONTH');
     
     console.log(campaign.getName()+ ', '+stats.getImpressions()+', '+stats.getConversionRate())
     
  }

it always return 0 as Conversion Rate. but it should be 9.09 according to my data set.

I tried logging stats object too, seems the field related to ConversionRate is not even there.

output of console.log(stats)

{ metrics: 
   { clicks: '11',
     videoViews: '0',
     conversions: 1,
     costMicros: '10520000',
     ctr: 0.125,
     averageCpc: 956363.6363636364,
     averageCpm: 119545454.54545455,
     impressions: '88' } }

this what I see from the ad report front end

this is the API guide I’m using
https://developers.google.com/google-ads/scripts/docs/reference/adsapp/adsapp_stats#getConversionRate_0

what am I doing wrong here ?