Попробуйте без помогашки, вот так:

$token = 'токен нельзя палить';

$paramGet = [
    "id" => (string)(1000 * time()),
    "sum" => [
        "amount" => 8,
        "currency" => "643"
    ],
    "paymentMethod" => [
        "type" => "Account",
        "accountId" => "643"
    ],
    "comment" => "Testing",
    "fields" => [
        "account" => "+79114353887"
    ]
];
$dataPostParam = json_encode($paramGet, JSON_UNESCAPED_UNICODE);

$ch = curl_init("https://edge.qiwi.com/sinap/api/v2/terms/__idPROVIVER__/payments");
curl_setopt($ch, CURLOPT_HTTPHEADER, array(
        'Content-Type: application/json',
        'Accept: application/json',
        'Authorization: Bearer ' . $token
    )
);
curl_setopt($ch, CURLOPT_CUSTOMREQUEST, "POST");
curl_setopt($ch, CURLOPT_POSTFIELDS, $dataPostParam);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
$sResponse = curl_exec($ch);

Там где __idPROVIVER__ это идентификатор провайдера, см документацию.