The advice from the experienced travellers in the community is to use other ways to make reservations than the Interrail/Eurail website. You can look at the guide in the link:

https://community.eurail.com/train-connections-reservations-47/how-to-get-reservations-105

If you, after having looked at the guide, have questions about how to make specific reservation, please give your travel details (departure date, time and route) preferably in a new post, and you will get advice. 

However I understand that VY-SE does not allow seat-only REServ. Can sometimes still be done via sj.se- but DO read howtodo-google is your friend and its easy once you know

Many reservations (except for French trains) can also be done via DB, at the ticket office or by phone.