I meant create a transaction (auth, capture...) for an existing order that has no payment yet.
I found the answer, here it is:
public function addTransactionToOrder($order, $paymentData = array()) {
try {
// Prepare payment object
$payment = $order->getPayment();
$payment->setMethod('my_payment_method');
$payment->setLastTransId($paymentData['id']);
$payment->setTransactionId($paymentData['id']);
$payment->setAdditionalInformation([Transaction::RAW_DETAILS => (array) $paymentData]);
// Formatted price
$formatedPrice = $order->getBaseCurrency()->formatTxt($order->getGrandTotal());
// Prepare transaction
$transaction = $this->transactionBuilder->setPayment($payment)
->setOrder($order)
->setTransactionId($paymentData['id'])
->setAdditionalInformation([Transaction::RAW_DETAILS => (array) $paymentData])
->setFailSafe(true)
->build(Transaction::TYPE_CAPTURE);
// Add transaction to payment
$payment->addTransactionCommentsToOrder($transaction, __('The authorized amount is %1.', $formatedPrice));
$payment->setParentTransactionId(null);
// Save payment, transaction and order
$payment->save();
$order->save();
$transaction->save();
return $transaction->getTransactionId();
} catch (Exception $e) {
$this->messageManager->addExceptionMessage($e, $e->getMessage());
}
}
