The Pass Cover Number you get from Customer Support through this form.

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 mention the start date of your travel when you contact Customer Support .

You can book the Eurostar by phone at SNCF. No need of Pass Cover Number. 

https://www.sncf.com/en/customer-service/contact-us/telephone

 Press #85 for English, no booking fees, reservations are sent via e-mail.

Thank you. I contacted the number and was told to contact Eurostar which was not accepting calls due to high volume. In order to book on E-europe i need a Pass Cover Number. Any idea. How to get it , request to Eurail has been filled out.

thanks

Did they say why? SNCF can definitely book Eurostar reservations. Also by phone.

They just said i need to contact Eurostar. And Eurostar systems were busy. I will try again today.

thank you