Hi, found this while investigating a different issue (Codex Vercel plugin not available for install), and ive found that the command that appears in this web is incorrect for codex to install the vercel plugin, the copyable text just lists available plugins in Codex.
Hey, @guillermovillarsanch! Welcome to the Vercel Community 
I took a look and found that this command is correct.
You need to scroll down to Vercel to then install it.