Permalinks and subdirectory

I have a WP installation with the home page as a page. This all works ok.

I want to move posts to a subdirectory called “blog”. I have modified the permalink by adding /blog/ to the start of it. I can now view single posts ok but i cant get to the list of posts, i get the 404 file, what do i need to do to get the list of posts, i.e. when the url is https://mysite/blog