I'm building some form data, populating it with arrays, and sending it over POST, via:

```
let fd = new FormData();
for (section in this.data.choices) {
    let key = section+(this.data.choices[section] instanceof Array ? '[]' : '');
    fd.append(key, this.data.choices[section]);
}
fetch('?get=plan', {method: 'post', body: fd}) //...

```

Here's the structure of `this.data.choices`:

```
{
    "mode": "o7ew4xqybwt",
    "packages": [
        "wx2xv1cakbe"
    ],
    "usertypes": [
        "s"
    ],
    "subjects": [
        "bxn5g1igm4l",
        "u1osgpv37fl",
        "q2scwqb27k7",
        "fl9riri0wpr"
    ]
}

```

However on the receiving side, in PHP, the arrays are arriving flattened. print\_r($\_POST) gives:

```
Array
(
    [mode] => o7ew4xqybwt
    [packages] => Array
        (
            [0] => wx2xv1cakbe
        )
    [usertypes] => Array
        (
            [0] => s
        )
    [subjects] => Array
        (
            [0] => bxn5g1igm4l,u1osgpv37fl,q2scwqb27k7,fl9riri0wpr
        )
)

```

It's no doubt something simple I'm missing but any help would be appreciated.