You do NOT have to activate it to make REServations-and its also much better and cheaper too to do it via other ways-see overveiw per country by seewulf.
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.
