I put four cards in to test it and it got stuck. I tried to align the cards but that didn't work either. I then used Twizzer to rip out the cards and try a card. It turns out that I just have to press the lever very hard, the more cards -> the stronger. I bought the gray color thinking it would look "silver" but it looks dark brown. The promotional image was illuminated with bright light, making it look "silver" to me.
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