Do they ask for the Pass Number or the Pass Cover Number?

Those are 2 different numbers.

They ask for the Pass Cover Number and i don’t know what it is and the difference between 

Do you have a mobile pass or a paper pass?

Grimaldi want a pass cover number. If you don't have one because you have a mobile pass, then you need to request one from customer service.

Strangely, Grimaldi Lines are missing on the benefits portal.

Yes i have a mobile pass. I ask the costumer service.

Thank you !

@rian: there are several other ferries also missing from the ´discount´ list, f.e. UNity line PL-Ystad/SE.

A few others have been mentioned here as not giving discount anymore (Eckeroe HEL-EE)

Where did you see any indication that they give a discount? Their website does not contain "Interrail” or "Eurail” anywhere.

I saw the information on their website :  https://www.grimaldi-lines.com/it/partner/interrail-2/

@Unity-got this myself last yr/autumn- so maybe it has now been scrapped.

Or if you really want to be 100%-go through the booking process. It was (if I remember 10%)-but ju/senior also get this and you cannot combine, so it did not bring me much. There were in fact 3 different ferries running from Swino-ujscie to Sverige. This one was cheaper as they charge much less for beds.

For your information: both Grimaldi and Minoan lines have been added and are now visible on the benefits portal.