Many RAR archives are encrypted. Check the source where you downloaded the file for the required password.
When a file is too large for a single upload (like a 50GB game or a 4K film), creators split it into smaller chunks. is the "header" file. odissey.part1.rar
If the extraction stops and asks for "Part X," it means that file is either missing from the folder or has been renamed. Many RAR archives are encrypted