My Code:
        ->pipe(new Group(array(
            "by"=>"SM_CODE",
			)))
        ->pipe(new CalculatedColumn(array(
            "Difference"=>function($row){
					$result = $row["SALESCYA"] - $row["SALESLYA"];
					$result=round($result);
					//if($result < 0) return "( ".$result." )";
					if(is_infinite($result) || is_nan($result)){$result = 0;}
					return $result;
            },
        ->pipe(new ColumnMeta(array(
            "Difference"=>array(
                //"type"=>"number",
                //"prefix"=>''
            ),
MyReportExcel.view
---------------------------
<?php
    use \koolreport\excel\Table;
    use \koolreport\excel\PivotTable;
    use \koolreport\excel\BarChart;
    use \koolreport\excel\LineChart;
use \koolreport\processes\ColumnMeta;
use \koolreport\processes\CalculatedColumn;
use \koolreport\processes\DateTimeFormat;
use \koolreport\processes\CopyColumn;
use \koolreport\processes\Group;
    $sheet1 = "Sales by Customer";
?>
<meta charset="UTF-8">
<meta name="description" content="Free Web tutorials">
<meta name="keywords" content="Excel,HTML,CSS,XML,JavaScript">
<meta name="creator" content="John Doe">
<meta name="subject" content="subject1">
<meta name="title" content="title1">
<meta name="category" content="category1">
<div sheet-name="<?php echo $sheet1; ?>">
    <?php
    $styleArray = [
        'font' => [
            'name' => 'Calibri', //'Verdana', 'Arial'
            'size' => 30,
            'bold' => false,
            'italic' => FALSE,
            'underline' => 'none', //'double', 'doubleAccounting', 'single', 'singleAccounting'
            'strikethrough' => FALSE,
            'superscript' => false,
            'subscript' => false,
            'color' => [
                'rgb' => '000000',
                'argb' => 'FF000000',
            ]
        ],
        'alignment' => [
            'horizontal' => 'general',//left, right, center, centerContinuous, justify, fill, distributed
            'vertical' => 'bottom',//top, center, justify, distributed
            'textRotation' => 0,
            'wrapText' => false,
            'shrinkToFit' => false,
            'indent' => 0,
            'readOrder' => 0,
        ],
        'borders' => [
            'top' => [
                'borderStyle' => 'none', //dashDot, dashDotDot, dashed, dotted, double, hair, medium, mediumDashDot, mediumDashDotDot, mediumDashed, slantDashDot, thick, thin
                'color' => [
                    'rgb' => '808080',
                    'argb' => 'FF808080',
                ]
            ],
            //left, right, bottom, diagonal, allBorders, outline, inside, vertical, horizontal
        ],
        'fill' => [
            'fillType' => 'none', //'solid', 'linear', 'path', 'darkDown', 'darkGray', 'darkGrid', 'darkHorizontal', 'darkTrellis', 'darkUp', 'darkVertical', 'gray0625', 'gray125', 'lightDown', 'lightGray', 'lightGrid', 'lightHorizontal', 'lightTrellis', 'lightUp', 'lightVertical', 'mediumGray'
            'rotation' => 90,
            'color' => [
                'rgb' => 'A0A0A0',
                'argb' => 'FFA0A0A0',
            ],
            'startColor' => [
                'rgb' => 'A0A0A0',
                'argb' => 'FFA0A0A0',
            ],
            'endColor' => [
                'argb' => 'FFFFFF',
                'argb' => 'FFFFFFFF',
            ],
        ],
    ];
    ?>
    <div cell="A1" range="A1:H1" excelstyle='<?php echo json_encode($styleArray); ?>' >
        Sales Report
    </div>
    <div>Orders</div>
    <div>
        <?php
    Table::create(array(
        "dataSource"=>$this->dataStore('sales'),
        "grouping"=>array(
            "R_DESC"=>array(
                "calculate"=>array(
                    "{currentActual}"=>array("sum","SALESCYA"),
                    "{lastActual}"=>array("sum","SALESLYA"),
                    "{currentBudget}"=>array("sum","SALESCYB"),
                    "{currentDifference}"=>array("sum","Difference"),
                    "{currentPerDifference}"=>array("sum","PerDifference"),
                    "{currentRequire}"=>array("sum","Require"),
                    "{currentPerRequire}"=>array("sum","PerRequire"),
                ),
                "top"=>"<b>Region : {R_DESC}</b>",
                "bottom"=>"<td><b>Total</b></td><td></td><td></td><td style='text-align:right;'><b>{currentActual}</b></td><td style='text-align:right;'><b>{lastActual}</b></td><td style='text-align:right;'><b>{currentDifference}</b></td><td style='text-align:right;'><b>{currentPerDifference}</b></td><td style='text-align:right;'><b>{currentBudget}</b></td><td style='text-align:right;'><b>{currentRequire}</b></td><td style='text-align:right;'><b>{currentPerRequire}</b></td>",
            ),
        ),
        "sorting"=>array(
            "R_DESC"=>"asc"
        ),
        "showFooter"=>true,
        "columns"=>array(
            "SM_CODE"=>array(
                "label"=>"Salesman Code",
                "footerText"=>"<b>Grand Total</b>"
            ),
            "STYPE_DESC"=>array(
                "label"=>"Sub Category",
            ),
            "SM_NAME"=>array(
                "label"=>"Name",
            ),
            "SALESCYA"=>array(
                "label"=>"2021 Net Sales",
                "footer"=>"sum",
                "footerText"=>"<b>@value</b>",
				"cssStyle"=>"text-align:right;width:8em",
				"thousandSeparator" => ","
            ),
            "SALESLYA"=>array(
                "label"=>"2020  Net Sales ",
                "footer"=>"sum",
                "footerText"=>"<b>@value</b>",
				"cssStyle"=>"text-align:right;width:8em",
				"thousandSeparator" => ","
            ),
			
			
            "Difference"=>array(
                "label"=>"Difference",
                "footer"=>"sum",
                "footerText"=>"<b>@value</b>",
				"cssStyle"=>"text-align:right;width:8em",
				"thousandSeparator" => ","
            ),
			
/*			array(
				"label"=>"Difference",
				"value"=>function($row) {
					$result = $row["SALESCYA"] - $row["SALESLYA"];
					$result=round($result);
					if($result < 0) return "( ".$result." )";
					return $result;
				},
                "footer"=>"sum",
                "footerText"=>"<b>@value</b>",
				"cssStyle"=>"text-align:right;width:8em",
				"thousandSeparator" => ","
			),
*/		
/*			array(
				"label"=>"% of Diff",
				"value"=>function($row) {
					$result = round($row["SALESCYA"]) - round($row["SALESLYA"]);
					$result =round($result, PHP_ROUND_HALF_UP);
					$percentage = (($result) / round($row["SALESLYA"]));
					$percentage=round($percentage);
					if($percentage < 0) return "( ".$percentage." )";
					return $percentage;
				},
                "footer"=>"sum",
                "footerText"=>"<b>@value</b>",
				"cssStyle"=>"text-align:right;width:8em",
				"thousandSeparator" => ","
			),
*/			
            "PerDifference"=>array(
                "label"=>"% of Diff",
                "footer"=>"sum",
                "footerText"=>"<b>@value</b>",
				"cssStyle"=>"text-align:right;width:8em",
				"thousandSeparator" => ","
            ),
			
            "SALESCYB"=>array(
                "label"=>"2021 Sales Target",
                "footer"=>"sum",
                "footerText"=>"<b>@value</b>",
				"cssStyle"=>"text-align:right;width:8em",
				"thousandSeparator" => ","
            ),
/*			array(
				"label"=>"Require to Ach.",
				"value"=>function($row) {
					$result = $row["SALESCYB"] - $row["SALESCYA"];
					$result =round($result);
					if($result < 0){ return "( ".$result." )"; }
					else{
					return $result;
					}
				},
                "footer"=>"sum",
                "footerText"=>"<b>@value</b>",
				"cssStyle"=>"text-align:right;width:8em",
				"thousandSeparator" => ","
			),
*/
            "Require"=>array(
                "label"=>"Require to Ach",
                "footer"=>"sum",
                "footerText"=>"<b>@value</b>",
				"cssStyle"=>"text-align:right;width:8em",
				"thousandSeparator" => ","
            ),
			
/*			array(
				"label"=>"% of Ach.",
				"value"=>function($row) {
					$result = $row["SALESCYB"] - $row["SALESCYA"];
					$result =round($result, PHP_ROUND_HALF_UP);
					$percentage = (($result) / $row["SALESCYA"]);
					$percentage=round($percentage,2);
					if($percentage < 0) return "( ".$percentage." )";
					return $percentage;
				},
                "footer"=>"sum",
                "footerText"=>"<b>@value</b>",
				"cssStyle"=>"text-align:right;width:8em",
				"thousandSeparator" => ","
			),
*/			
			
            "PerRequire"=>array(
                "label"=>"% of Ach.",
                "footer"=>"sum",
                "footerText"=>"<b>@value</b>",
				"cssStyle"=>"text-align:right;width:8em",
				"thousandSeparator" => ","
            ),
        ),
        "cssClass"=>array(
            "table"=>"table-bordered",
            "tf"=>"darker"
        )
    ));
        ?>
    </div>
    
</div>
Query Result:

But After exporting excel file - Excel says
