Here is a reply you can follow that came from Amazon
I told you must leave a space after your comma in the keywords. if you don’t do amazon will picks the whole box up as one keyword.
The man explained that he tested my keywords and as an example he searched “slot-in slot in” and my product came up on amazon, the keywords looked like this “slot-in,slot in”
I think this is very important if this is the case and i noted that your article does not show spaces between your commas and keywords.
This came from Amazon support.
Currently a potential buyer would have to search for “Slot in slot in 3ds stylus touch stylus pen” as an example because i have setup my search terms wrong!
I hope this is useful to you, its certainly useful to me as currently most of my keywords are completely useless as there are no spaces.