transactionFee parameter does nothing

[clawfire]

I'm trying to use stripe connect and I saw I should be able to set a transactionFee but it does nothing in my case.

$this->transaction_data = [
    'amount' => $order_total,
    'currency' => $event->currency->code,
    'description' => 'Order for customer: ' . $order_email,
    'paymentMethod' => $this->options['paymentMethod'],
    'receipt_email' => $order_email,
    'returnUrl' => $returnUrl,
    'confirm' => true,
    // Add the configured payment gateway fees to the existing fees.
    'transactionFee' => $gateway_fees + $fees ,
    // Pass the destination ID
    'destination' => $account_payment_gateway['transfer_data_destination_id']
];

The transaction transfer to the connected account works well, but the transactionFee isn't used.

Stripe's log on the /v1/payment_intentsshow no sign of application_fee parameters:

{
  "amount": "1672",
  "currency": "eur",
  "description": "Order for customer: clawfire@gmail.com",
  "transfer_data": {
    "destination": "acct_1JXXL0JqGbicBCJ7"
  },
  "receipt_email": "clawfire@gmail.com",
  "payment_method": "pm_1JpfVzDhKAJibjYZurgJEjSk",
  "confirmation_method": "manual",
  "capture_method": "manual",
  "confirm": "true",
  "return_url": "https://tickets.out.lu/e/4/checkout/success?is_payment_successful=1"
}

Also, transactionFee show nowhere in the entire codebase