如何在PHP中将多个复选框值插入CSV

Question

I'm trying to insert multiple checkbox values with the same names into a CSV with PHP but it doesn't populate the CSV unless it's a single checkbox.

date_default_timezone_set('Europe/London');
$dateNow = date('m/d/Y h:i:s a', time());
$data = [];
$q1ch = implode(",", $_POST["business-related-purchases[]"]); // this is the checkbox I am trying to push into the CSV

$fields = ['contactId', 'date', 'firstName', 'lastName', 'emailAddress', 
            'companyName', 'q1', $q1ch, 'main-reasons', 'q2', 'sell-promote-radio', 
            'q3', 'researched-information', 'q4', 'q5', 'tyres-online'
        ];

foreach ($fields as $field) {
    if (isset($_POST[$field])) {
        $data[] = trim($_POST[$field]);
        // die (print_r  ($data[]));
    } else {
        $data[] = '';
    }
}

I have tried just inserting 'business-related-purchases directly into the array without putting it in a variable.

<input value="Banking" type="checkbox" class="banking" name="business-related-purchases">
<input value="Equipment" type="checkbox" name="business-related-purchases">

and these are my checkboxes. I have also tried inserting [] at the end of names e.g. name="business-related-purchases[]"