seat reservations split on site HZPP

Hi everyone, I saw that a lot of people here have questions about the seat reservations to Split. I want to take the train in the beginning of May to Split from Zagreb. As you probably know, seat reservations are required and you’re not able to book them on the Interrail site. I saw it was advised a lot to book a train seat when you’re in Croatia. however, I fear that I won't be able to get a place then, so im looking for other ways to get a seat reservation. I saw on the site of Croatian railways ( https://prodaja.hzpp.hr/en ) that you can book tickets for the train I would like to get. however, I nowhere see an option to enter that I have an interrail pass. I only see discounts for youth/students. Is that the same? Or is it unnecessary to book ahead anyway because there will be enough seats in every instance?

thanks in advance :)