I want update an Users Balance but i dont know how i can do it.
With my code its dont work:

```
 $sql = "UPDATE apiusers SET balance = balance - (product_price) WHERE username = (username);";
if(mysqli_query($link, $sql)){
    echo "Records added successfully.";
} else{
    echo "ERROR: Could not able to execute $sql. " . mysqli_error($link);
}

```

Table apiuser:

```
+-------------+
| Field       | 
+-------------+
| id          | 
| user        |
| pass        | 
| balance     |
| lastip      | 
| lastlogind  |
| email       |
| verification|
+-------------+

```