Updating meta_value in a custom key

Question

I have a custom meta_key called 'sales' this holds information of all sales a sales person has carried out along with a flag to say if it has been authorised, awaiting authorisation or if it has been rejected.

Wordpress is saving each sale as a separate row in the usermeta table, which I don't have an issue with what I am stuck on is updating a specific sales status; i.e changing it from pending (2), to either rejected (0) or approved (1).

I have tried a few ways to do this following advice on other forums etc but it seems like I may be storing the meta data incorrectly in the first place as all the examples are amusing that there is only on row per custom meta_key per user; so the posts are suggesting to update the value, delete all data associated with the key then to upload the modified array.

I currently have the following code but it isn't working as I'd imagined as it is saving the data into another array so becoming further nested.

if(isset($_POST['approved'])) {

    $saleStatus = 2;

    switch ($_POST['approved']) {
        case 'approve':
            $saleStatus = 1;
            break;

        case 'reject':
            $saleStatus = 0;
            break;
    }

    $sales = get_user_meta($_POST['repID'], 'sales');

    foreach ($sales as $key => $sale) {

        if($sale['reg'] === $_POST['carReg']) {

            $sales[$key]['approved'] = $saleStatus;

        }

    }

    update_user_meta( $_POST['repID'], 'sales', $sales);
}

UPDATED

$sales = get_user_meta($_POST['repID'], 'sales', true);

foreach ($sales as $key => $value) {
  if($value === $_POST['carReg']) {
    $sales[0]['approved'] = $saleStatus; //This is overwriting all meta_values making them duplicates
 }
}

update_user_meta( $_POST['repID'], 'sales', $sales);

ADDING SALE

if(isset($_POST['customer-name']) && isset($_POST['make']) && isset($_POST['model']) && isset($_POST['reg']) && isset($_POST['condition'])) {

    $branch         = sanitize_text_field($GLOBALS['user_rep']['repBranch']);
    $customer_name  = sanitize_text_field($_POST['customer-name']);
    $make           = sanitize_text_field($_POST['make']);
    $model          = sanitize_text_field($_POST['model']);
    $reg            = sanitize_text_field($_POST['reg']);
    $condition      = sanitize_text_field($_POST['condition']);

    $newSales = array(
            'branch' => $branch,
            'customer_name' => $customer_name,
            'make' => $make,
            'model' => $model,
            'reg' => $reg,
            'condition' => $condition,
            'time' => time(),
            'approved' => 2
        );

    update_user_meta(wp_get_current_user()->ID, 'sales', $newSales);    
}

Answer 1

The problem is this line

$sales = get_user_meta($_POST['repID'], 'sales');

change it to

$sales = get_user_meta($_POST['repID'], 'sales', true);

The last parameter says, that you are getting a single value - an array. Otherwise you get an array inside another array.

https://developer.wordpress.org/reference/functions/get_post_meta/

EDIT: After reading the comments, as you have the meta in multiple rows, you should do update_post_meta in the foreach loop:

$sales = get_user_meta($_POST['repID'], 'sales');

foreach ($sales as $key => $sale) {
    $old_sale_data = $sale;
    if($sale['reg'] === $_POST['carReg']) {
        $sale['approved'] = $saleStatus;
         update_user_meta( $_POST['repID'], 'sales', $sale, $old_sale_data);
    }
}

https://codex.wordpress.org/Function_Reference/update_post_meta

Btw., saving the sales as user meta in array isn't a great idea, unless everything you're going to do with the data is displaying it. Doing queries on the data, searching, reporting, all that will be almost impossible with data saved this way. You'd be better creating a custom post type sales ad saving the meta for each of the sale, or even better creating a separate db table for sales...