ePay payment plugin - callback fails with error 500

-- HikaShop version -- : 4.6.1
-- Joomla version -- : 4.1.4
-- PHP version -- : 8.0

Hi

I've bought your ePay payment plugin to use with recurring subscriptions. I've setup a test account at ePay/Bambora and added my server IP + domain in their control panel. My problem is, that the callback is not received by Hikashop. In my server log, I see that the callback results in a server error with code 500.

54.154.212.155 - - [28/Jul/2022:15:21:21 +0200] "GET /index.php?option=com_hikashop&ctrl=checkout&task=notify¬if_payment=bambora&tmpl=component&lang=da&Itemid=123&txnid=332727729&orderid=3&amount=100000¤cy=208&date=20220728&time=1320&txnfee=0&subscriptionid=16610366&paymenttype=1&cardno=444444XXXXXX4000&hash=b0b70d9ae4d95bc24e25ecb2ae159077 HTTP/1.1" 500 6715 "-" "-"

54.77.224.116 - - [28/Jul/2022:16:09:24 +0200] "GET /index.php?option=com_hikashop&ctrl=checkout&task=notify¬if_payment=bambora&tmpl=component&lang=da&Itemid=123&txnid=332738932&orderid=8&amount=10000¤cy=208&date=20220728&time=1609&txnfee=0&paymenttype=1&cardno=444444XXXXXX4000&hash=ad301cd67559cbb610f9d5ded85af1a9 HTTP/1.1" 500 2030 "-" "-"

From ePay callback response I see this error message: Attempt to assign property "txn_id" on null
Edit: Activated debug in Joomla and the stack trace points to JROOT/plugins/hikashoppayment/bambora/bambora.php:319

From the payment log:
Bambora transaction id: 332738250
07.28.22 14:01:54

Array
(
[option] => com_hikashop
[ctrl] => checkout
[task] => notify
[notif_payment] => bambora
[tmpl] => component
[lang] => da
[Itemid] => 123
[txnid] => 332738250
[orderid] => 6
[amount] => 100000
[currency] => 208
[date] => 20220728
[time] => 1559
[txnfee] => 0
[subscriptionid] => 16610868
[paymenttype] => 1
[cardno] => 444444XXXXXX4000
[hash] => 4a8ac4d3e8725d814e32de6d9341f667
)

EDIT again: on line 279 I changed $order_payment_params = null; to $order_payment_params = new stdClass();
Seems to have fixed the issue with the callback.

Another thing - there is an untranslated language constant "HANDLE_NO_RECURRING" - not sure what that setting is for?