I had to use about 10 guitar picks. The case “clips” are amazingly tight. I’d get one in just barely, then I’d add another in the now-opened slot. Then another. I’d space them about 1 or 1.5cm apart on two sides. Work into a corner and it will release. (I’m going on memory. I bought packs of the cheapest guitar picks. I have both thin and medium. I think I used medium, but I can’t remember.)
I had to use about 10 guitar picks. The case “clips” are amazingly tight. I’d get one in just barely, then I’d add another in the now-opened slot. Then another. I’d space them about 1 or 1.5cm apart on two sides. Work into a corner and it will release. (I’m going on memory. I bought packs of the cheapest guitar picks. I have both thin and medium. I think I used medium, but I can’t remember.)