As with all my craft projects, it took me several months but finally I finished it:
I changed the pattern slightly as I was supposed to knit a separate band, to twist it in a particular manner and to sew it to the lower part of the vest. It was a lot of headache so I gave up and added the finishing touch with the help of a crochet hook.
Here is how it was supposed to look:
Not exactly the same thing, but in general, I'm content!