Display R2 in GEE chart

I have created scatter plot in GEE but for some reason it doesn’t display the R2 and the way the linear regression displayd is also not good:

as you can see. the R2 isn’t displayed at all and the linear regression has NDVI inside it.

This is the code I have used:

// Generate chart from sample
var chart = ui.Chart.feature.byFeature(sample, 'SAR', 'NDVI')
    .setChartType('ScatterChart')
    .setOptions({title: "NDVI vs SAR(db)", pointSize: 3,
    legend: {maxLines: 5, position: 'top'},
    series: {
          0: {targetAxisIndex: 0},
          1: {targetAxisIndex: 1}
        },
        vAxes: {
          // Adds titles to each axis.
          0: {title: 'NDVI'},
          1: {title: 'NDVI '}
        },
                hAxes: {
          // Adds titles to each axis.
          0: {title: 'db'},
          1: {title: 'db '}
        },
    trendlines: {
        0: {
          type: 'linear',
          color: 'lightblue',
          lineWidth: 3,
          opacity: 0.7,
          showR2: true,
          visibleInLegend: true
        },

      },
});

As you can see, the showR2 is true, what is the mistake?