The source may have been deleted.

As @Please call me Wang Er said, you can view the current source list:

gem sources
# 或
gem sources -l

Or join Taobao’s ruby ​​mirror source:

gem sources -a http://ruby.taobao.org/

Let’s take a look at the current source first: gem source

It should be http, try changing it to http?

gem source See what string the source is (it should be https://rubygems.org/ with a slash at the end)

Then execute gem source --remove https://rubygems.org/

It’s because I’m missing the trailing slash and I don’t have enough reputation to give likes to others

You’re right, there’s a slash/