Adding a repo from `.flatpakrepo` file does not work

When opening a .flatpakrepo file in PureOS Store, a window that allows to add the repo pops up - however, tapping the "Install" button does nothing and prints this into the logs:

Sep 27 17:37:19 evergreen gnome-software[3311]: gs_plugin_app_install: assertion 'gs_app_get_kind (app) != AS_COMPONENT_KIND_REPOSITORY' failed
Sep 27 17:37:19 evergreen gnome-software[3311]: flatpak did not set error for gs_plugin_app_install
Sep 27 17:37:19 evergreen gnome-software[3311]: g_str_has_prefix: assertion 'str != NULL' failed
Sep 27 17:37:19 evergreen gnome-software[3311]: g_str_has_prefix: assertion 'str != NULL' failed