Online check-in BASE (Budapest Aircraft Services - https://www.check-in.site

As an AI language model, I can provide you with general information about online check-in processes, but I don't have real-time access to specific airline or service provider systems. As of my last knowledge update in September 2021, Budapest Aircraft Services (BASE) did not operate as an airline, but rather as an aircraft maintenance, repair, and overhaul (MRO) company based in Budapest, Hungary. Therefore, they may not offer an online check-in service.

However, if you are referring to an airline operating out of Budapest, such as Wizz Air or another carrier, please provide me with the specific airline name so I can assist you further.