Updating yii2 Select2 ID in yii2-dynamicform

[Spywavenoah]

Hello Guys,
I have a Sales form that was created using yii2-dynamicform which is forming fine. but I want to be able to pass the unit price of a product selected to corresponding input field that is also added dynamically, how do i add the id of input element to select2 dynamically base on the numbers of record?
from what i ahve done so far, it keeps updating the unit price of the first row only

'dynamicform_wrapper', // required: only alphanumeric characters plus "_" [A-Za-z0-9_] 'widgetBody' => '.container-items', // required: css class selector 'widgetItem' => '.item', // required: css class 'limit' => 4, // the maximum times, an element can be cloned (default 999) 'min' => 1, // 0 or 1 (default 1) 'insertButton' => '.add-item', // css class 'deleteButton' => '.remove-item', // css class 'model' => $BranchSales[0], 'formId' => 'dynamic-form', 'formFields' => [ 'pump', 'product_material_name', 'attendant', 'amount', 'qty', ], ]); ?>

        <div class="container-items"><!-- widgetContainer -->
        <?php $r=0; foreach ($BranchSales as $index => $SalesEntries): $r++;?>

            <div class="item card card-warning"><!-- widgetBody -->
                <div class="card-header">
                    <h3 class="card-title pull-left">Attendant <?= ($index + 1) ?></h3>

                    <div class="float-right">
                        <button type="button" class="add-item btn btn-success btn-xs"><i class="fa fa-plus"></i></button>
                        <button type="button" class="remove-item btn btn-danger btn-xs"><i class="fa fa-minus"></i></button>
                    </div>
                    <div class="clearfix"></div>
                </div>
                <div class="card-body">
                    <?php
                        // necessary for update action.
                        if (! $SalesEntries->isNewRecord) {
                            echo Html::activeHiddenInput($SalesEntries, "[{$index}]id");
                        }
                    ?>
                    <div class="row">


        <div class="col-sm-1">
        <?= $form->field($SalesEntries, "[{$index}]pump")->textInput(['maxlength' => true]) ?>
        </div>

        <div class="col-sm-4">
                            <?= $form->field($SalesEntries, "[{$index}]attendant")->widget(Select2::classname(), [
            'data' =>$data, 
                // ['prompt'=>'-Choose a Product-'],
                'language' => 'en',
                 'options' => [
        'prompt' => 'Select Pump Attendant']
]); ?>
                        </div>


                        <div class="col-sm-4">
                            <?= $form->field($SalesEntries, "[{$index}]product_material_name")->widget(Select2::classname(), [
            'data' =>ArrayHelper::map(GoodsProducts::find()->where(['branch_code'=>Yii::$app->user->identity->branch_code])->asArray()->all(), 'product_material_code', 'product_material_name'), 
                // ['prompt'=>'-Choose a Product-'],
                'language' => 'en',
                'id' => '[{$index}]product_material_name',
                 'options' => [
        'prompt' => 'Select Product',
    'onchange'=>'
                    $.post( "'.urldecode(Yii::$app->urlManager->createUrl('branch-sales/list&id=')).'"+$(this).val(), function( data ) {
                                         $( "Input#branchsales-'.$index.'-u_price" ).val(data); //here is where am having issues, it keeps updating the first one only
                      
                    });
                ']
]); 

?> </div>

field($SalesEntries, "[{$index}]u_price")->textInput(['maxlength' => true]) ?>

                        <div class="col-sm-1">
                            <?= $form->field($SalesEntries, "[{$index}]qty")->textInput(['maxlength' => true,'onkeyup' => 'totales($(this))']) ?>
                        </div>

 </div><!-- .row -->
                </div>
            </div>
        <?php endforeach; ?>
        </div>
        <?php DynamicFormWidget::end(); ?>
    </div>
</div>