customer notification not send after status update

-- url of the page with the problem -- : www.cultuuroudenbosch.nl/
-- HikaShop version -- : 6.5.0
-- Joomla version -- : 6.1.1
-- PHP version -- : 8.4

Hi,
We are using RO Payments for handling the payments and the return to HikaShop.

In here we set the status of the order to "Shipped" because it's about digital tickets.
I have updated the setting to always notify the customer when updating an order.

The problem is that this e-mail is not send when the status is updated via RO Payments but is when done manually.
Checked with Roland and he tells me that when the test are done and the statuses meet the requirements he execute this code :
$history->notified = 1;

Now can you help us figure out if anything is wrong with this approach?