Under visiting/traveling purpose, my type of visa is C. So what is your purpose of travel? Also, there are a few questions you need to thoroughly understand in order to be successfully granted a Schengen visa. Four big questions are about: Purpose, Length of stay, Financial situation, Education/work/family.
This post is for someone who is no longer a student and doesn’t have a job yet (by the time preparing for this visa), wants to travel for a long period of time but doesn’t have deep pocket, and a Vietnamese citizen (this one deeply matters: it’s painfully hard for a young Vietnamese citizen with countless restrictions).
My situation seems unrealistic, but how on earth was I issued a 90-day visa with multiple entries? So, stay with me!