Restoring a backup key

[Osama Khalid]

Hello,

When I generated my OpenPGP smartcard, I asked GPG to save a backup
version of the key. It did that in an
"sk_<random_letters_and_numbers>.gpg" file.

Now I'm trying to find a way to restore my secret key.

Currently, "$ gpg --list-secret-keys" has no output, but "$ gpg
--list-keys" does list the public key of my secret key.

Running "$ gpg --allow-secret-key-import --import sk_<...>.gpg"
returns in:
> gpg: key <secret_key_id>: no user ID
> gpg: Total number processed: 1
> gpg:       secret keys read: 1
And it does not import anything.

I was wondering about the correct way to do that.

Thank you!

--Osama Khalid