The browser console prints error 400 when making the request 'https://read.amazon.co.jp/renderer/render?'. If you modify the 'numPage' and set a low value, such as 4, then the script works.
I cant reproduce the failed request with error code 500 on Firefox with ViolentMonkey, the script works totally fine sometimes but also buggy sometimes, I cant figure out where the problem is by the moment.
The browser console prints error 400 when making the request 'https://read.amazon.co.jp/renderer/render?'.
If you modify the 'numPage' and set a low value, such as 4, then the script works.