when installing ezp, if a composer update is done before starting the setup wizard, when the packages are loaded from http://packages.ez.no/ the url searched is ezpublish/5.3/5.3.1/

this path does not exist, so no package list is created, and the page shows the error

Error
Retrieving remote site packages list failed. You may upload packages manually.
Remote repository URL: http://packages.ez.no/ezpublish/5.3/5.3.1/