[Trying to] Installing flatpak on Arch linux fails:
$ sudo pacman -S flatpak
resolving dependencies...
:: There are 3 providers available for xdg-desktop-portal-impl:
:: Repository extra
1) xdg-desktop-portal-gtk 2) xdg-desktop-portal-kde
:: Repository community
3) xdg-desktop-portal-wlr
Enter a number (default=1): 1
looking for conflicting packages...
Packages (11) appstream-glib-0.7.18-1 gcab-1.4-1 geoclue-2.5.7-3 geocode-glib-3.26.2-1
gnome-desktop-1:40.0-1 gnome-keyring-1:40.0-1 libstemmer-0+713-2 ostree-2021.1-1
xdg-desktop-portal-1.8.0-1 xdg-desktop-portal-gtk-1.8.0-1 flatpak-1.10.2-1
Total Download Size: 0.63 MiB
Total Installed Size: 29.29 MiB
:: Proceed with installation? [Y/n] Y
:: Retrieving packages...
error: failed retrieving file 'ostree-2021.1-1-x86_64.pkg.tar.zst' from mirror.rackspace.com : The requested URL returned error: 404
error: failed retrieving file 'ostree-2021.1-1-x86_64.pkg.tar.zst' from mirrors.evowise.com : The requested URL returned error: 404
error: failed retrieving file 'ostree-2021.1-1-x86_64.pkg.tar.zst' from mirror.rackspace.com : The requested URL returned error: 404
error: failed retrieving file 'ostree-2021.1-1-x86_64.pkg.tar.zst' from mirror.rackspace.com : The requested URL returned error: 404
warning: failed to retrieve some files
error: failed to commit transaction (failed to retrieve some files)
Errors occurred, no packages were upgraded.
What's the correct way to download and install flatpack on Linux?
Note that it is not advisable to install an individual package after -Sy or -Syy. If you need to update your mirrors with -y to install a package, you should combine it with a full system upgrade -u:
sudo pacman -Syu flatpak
You might not see immediate breakage with -Sy <package>, but eventually something will break with continued use. If <package> happens to pull in new lib versions, then any program that depends on those libs will break since they will still be built against the old libs.