The fact that you did buy a Eurail pass doesn't mean you are allowed to use every train in Europe - it has to be one of the participating train companies. 

Your screenshot does show an OUIGO train. OUIGO is a french low-cost rail service company which is not included. That's why you get this message.

You need to take one of SNCF's TGV trains on this route. The SNCF is France's national railway company.

BTW: The travel planner does show just not included trains for June 4th because the SNCF timetable for June has not been published yet (but the OUIGO timetable is). Use a date up to May 22nd to get an idea for SNCF's timetable for June. But you can't do a reservation yet.

You may enter your trip here https://www.sncf-connect.com/en-en/ and they will send you an Email when it's possible to book a reservation for June 4th.

Thank you so much for your response. I didn’t realize that the timetable was not published yet for those dates. That clarifies my concern. I appreciate your help!