Nighttrain Budapest - Bucharest count as one day Sometimes the app have struggle to count traveldays correct had the same issue (Happens because the train change in the non public timetables few times the trainnumber and for the Plannerapps it looks like a change after midnight)

Please note that there is currently no passengertrain traffic from Bulgaria to Turkey this means that even the direct Coach from Bucharest via Bulgaria to Istanbul is not running. Last station you can reach by rail is Swilengrad (next to the Greek/Bulgarian/Turkish border)

I thank you very much for your answer, I did not have this information in relation to the bosphorus express, is it in relation to the covid! is there another alternative to reach istanbul from svilengrade? and for the reservation of seats please how can I do? thank you so much

I'm not sure if there currently any passenger traffic is allowed to Turkey.

Which train(s) would you like to book? To be honest, I have never used the app for that because there are extra costs involved.

so you have to reserve the seats at the station !? I have to take the train between bucharest and istanbul (bosphorus express) which leaves at 11 am and arrives at 6:20 am

Bucharest - istanbul was very hard to reserve in advance online The bestoption before Covid was a travelagency in Budapest but they are no more. Bestway is yet at a Station. For sure in Romania with luck in Germany,Czech Republic or Hungary But i can´t find a actual timetable of this train and are 90% sure that this train is not running at the moment :/

For trains in the Balkan countries, I've often used Deutsche Bahn (travel agent or at a DB station) or at a local station. Some of those reservations still cannot be done online or in electronic format, so any online order would still have to be printed as a classic paper ticket and sent to you. Interrail can do that (via its website) but will charge another fee for mail delivery (on top of the 2 EUR fee per reservation)…

But first the train needs to run, as @seewulf already pointed out. I think it is stil temporarily suspended:

https://www.bdz.bg/bg/a/vremenno-se-spira-dvizhenieto-na-mezhdunarodniya-vlak-sofiya-istanbul

Turkish railways say their international trains are still not running because of the corona crisis:

https://www.tcddtasimacilik.gov.tr/trenler/uluslararasi-trenler/

thank you very much for your answer i was finally able to reserve a few seats i only have budapest - bucharest left which i can't find. I saw that the Turkish-Bulgarian border is closed I would wait the next few days to see otherwise I would adapt my trip by taking a plane from Sofia to istanbul. thank you so much

You probably have to do that at the station. Probably also possible in Germany or Austria and maybe in France.