If you try to extract and get an "Unexpected end of data" error, you are likely missing part .001 or subsequent parts.
You must have SS-JulSS-013_s.7z.001 in the same folder. If there are more parts (.003, .004), you need those too. The Software: Use 7-Zip (Windows) or Keka (Mac). SS-JulSS-013_s.7z.002
If extraction fails, one of the volumes might be corrupted. Many uploaders provide a .sfv or .md5 file to verify that every part is intact. If you try to extract and get an