Fastpages 'There isn't a GitHub Pages site here' forever

Good afternoon,
I’m sorry if there is already a solution to the problem I’m going to tell you about, but after searching the forum I haven’t found anything.
I am trying to create my own blog with “fastpages”. I follow the instructions, and even the video, but the result is always the same:

There isn't a GitHub Pages site here. ````

Likewise in "Actions" I get the following:
![Captura de pantalla (3)|690x194](upload://gfnAQhBzAfbJMgTXI6dMxJeUtn7.png)

Please, any idea to help me to solve the problem.