redirect and emacs say error in process filter: Invalid escape character syntax

[hjonline]

我用的是 windows 下的 emacs 26.2 ，用“(add-to-list 'package-archives '("popkit" . "https://elpa.popkit.org/packages/"))
访问时，只得到
”error in process filter: Invalid escape character syntax"
然后直接在浏览器中访问 https://elpa.popkit.org/packages/ ，出现重定向页面：
Package Listing

Please see the main page for a full package listing. You will be redirected automatically.
会不会是这个原因导致失败？