How to install refs from created usb for installing app?

[Yi-Soo An]

I have already made a usb with refs for gnome-builder.
But when I try to install it without internet connection, I got this error.

$ flatpak install --user flathub org.gnome.Builder//stable

error: Unable to load metadata from remote flathub: No such ref 
(org.flathub.Stable, ostree-metadata) in remote flathub or elsewhere


But when I tried remote-ls, it shows as below,

$ flatpak remote-ls file:///media/test/workshop/.ostree/repo
Ref
org.freedesktop.Platform.html5-codecs
org.gnome.Builder
org.gnome.Sdk
org.gnome.Sdk.Docs
org.gtk.Gtk3theme.Ambiance


Do I have to command this every single time when I wanna install it via usb?

$ flatpak remote-modify --collection-id=org.flathub.Stable flathub
$ flatpak update


I really have no idea what's the matter with it.

Thank you in advance.