Bari to Dubrovnik on Jadrolinija travelling 20 August

I have tried to book the ferry from Bari to Dubrovnik on 20 August. However, it does not allow for a seat or cabin option only deck space. Can you please advise if the seat and cabin is available and how I book it.
Also is it possible to take a suitcase.

I just tried to book and it shows no spaces in cabins for 20.08.
Cabins may be already fully booked for that date as I tried some other dates and it does shows cabin spaces available.
So at the moment for that date, you can only book deck space.
Yes, you can take suitcase with you.