Multiform with HTTP client

Hi all!

Moving from plain curl to the Laravel HTTP client I'm encountering an issue in the multiform. I'm trying to send this:

$payload  = [
            'data' => 'Belgium',
            'file' => new \CURLFILE(Storage::disk('local')->path('public/xxxx/xxxx.file'))
        ];

In plain curl it's working flawless, but when I try to use the attach() helper on the HTTP client, it doesn't allow me to send the complete $payload. Which is necessary for the endpoint I'm posting to.

Can someone give me a direction?

Curl code:

curl_setopt_array($curl, array(
            CURLOPT_URL => $path,
            CURLOPT_RETURNTRANSFER => true,
            CURLOPT_ENCODING => '',
            CURLOPT_MAXREDIRS => 10,
            CURLOPT_TIMEOUT => 0,
            CURLOPT_FOLLOWLOCATION => true,
            CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
            CURLOPT_CUSTOMREQUEST => 'POST',
            CURLOPT_POSTFIELDS => $payload,
            CURLOPT_HTTPHEADER => array(
                'Accept: application/json, text/javascript, */*; q=0.01',
                'Accept-Language: nl,en-US;q=0.7,en;q=0.3',
                'Accept-Encoding: gzip, deflate, br',
                'Referer: ' . $this->base_url . '/login',
                'X-Requested-With: XMLHttpRequest',
                'Csrf-Token: ' . Crypt::decrypt($token),
                'Origin: $this->base_url',
                'Connection: keep-alive',
                'Cookie: ' . Crypt::decrypt($cookie),
            ),
        ));

        $response = curl_exec($curl);

        curl_close($curl);