почему не срабатывает json_decode в PHP?

<? $courseDates = !empty($param['card_dates2']) ? json_decode($param['card_dates2']) : [];?>
                    <? $i = 0; ?>
                    <?foreach($courseDates as $courseDate){?>
                        <?if (strtotime($courseDate) > time()) {?>
                            <div class="c-style_display_flex c-style_align-items_center" style="margin-bottom: 10px;">
                                <span class="c-style_nowrap2"><?=$i + 1?> дата</span>
                                <input readonly data-id="<?=$i++ +1?>" style="margin-left: 5px;" class="j-datetimepicker" type="text" name="card_dates2[]" value="<?= $courseDate ?? '' ?>" placeholder="">
                            </div>
                        <?}?>
                    <?}?>
                    <div class="c-style_display_flex c-style_align-items_center" style="margin-bottom: 10px;">
                        <span class="c-style_nowrap2"><?=$i + 1?> дата</span>
                        <input readonly data-id="<?=$i++ +1?>" style="margin-left: 5px;" class="j-datetimepicker last" type="text" name="card_dates2[]" placeholder="">
                    </div>