ここで引用符に問題があります。変更
$sqlCmd = sprintf("UPDATE account.account SET coins = coins +100 WHERE id = '.$_SESSION['user_id'].'"
と
$sqlCmd = "UPDATE account.account SET coins = coins +100 WHERE id = '".$_SESSION['user_id']."'"
ここで引用符に問題があります。変更
$sqlCmd = sprintf("UPDATE account.account SET coins = coins +100 WHERE id = '.$_SESSION['user_id'].'"
と
$sqlCmd = "UPDATE account.account SET coins = coins +100 WHERE id = '".$_SESSION['user_id']."'"