(url-insert-file-contents “http://127.0.0.1:9999?test=1”) 

GET ?test=1 HTTP/1.1 MIME-Version: 1.0 Connection: keep-alive Host: 127.0.0.1:9999 Accept-encoding: gzip Accept: */* User-Agent: URL/Emacs Emacs/31.0.50 (TTY; x86_64-suse-linux-gnu)

Should it be /?test=1， Missing "/" This url complies with the RFC 3986 standard and can be handled normally in tools such as curl