Have you contacted Customer Support through this form and asked for the Pass Cover Number?

https://eurail.zendesk.com/hc/en-001/requests/new

Customer Support is currently overloaded with requests so you will probably have to be patient to get help. Please let Customer Support know what date your travel will start so that they can prioritise your request correctly.

For most routes there are different possibilities to make reservations and some don't require the Pass Cover Number.

If you give your travel details: date, departure time and route, here you can get advice on alternative ways to make your reservation. 

Thank you, @AnnaB ! 

I’ll give that a try - I know everyone in the industry is swamped right now...

If you give your travel details here you can get advice on ways to make reservations without the need of a Pass Cover Number.

Sure! My husband, daughter and baby (lap infant) are looking to travel from Paris to Girona, Spain on Saturday June 11. The 3 of us have rail passes that we purchased through Rail Europe.

I’ve been trying to get this taken care of for weeks as I know how fast these trains fill up in the summer!

You can generate a pass cover number here and you don’t need to contact customer service:

https://www.eurail.com/en/book-reservations#/generatePassCoverNumber?utm_source=chatbot&utm_campaign=pcn
You can access this by using the chat bot on the help page by typing pass cover number.