$day1 = date("d-m-Y");
$find = $db->prepare("
SELECT SUM(suma) FROM kot_payments WHERE data = :data AND ref_id = 10215
");
$find->execute(array('data' => $day1));
$row = $find->fetch();
if(!empty($row) && $row !== false){
$depref1 = $row['SUM(suma)'];
}
echo $depref1;
data = :data AND ref_id = 10215
.date("d-m-Y");
.$depref1
не определен.