It is recommended to exactly follow the steps as described in Missing vouchers from 2025 in Vouchers on Fortnox - #11, including a screenshot.
From the information in this screenshot the request ID could be distilled.
Till the second the itgenboe161 occurred, the system was still retrieving data.
It is recommended to try again and check the settings for timeout. As an alternative, the download can also be tried using curl as described on How do I use curl to execute an Invantive Cloud OData4 request?.