[afn]

By default, curl interprets braces and square brackets to expand into multiple URLs (similarly to bash and other shells). You can disable this, and use literal braces & brackets in URLs, by passing ‘-g’ (‘--globoff’).

[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.