[layer8]

Braces and square brackets (as well as double quotes) are not allowed unencoded in query strings, see the definition of pchar in https://datatracker.ietf.org/doc/html/rfc3986#section-3.4.

[__s__]

That's true. Although it will make the URL longer, I have decided to use encodeURIComponent to escape characters and avoid potential bugs.