Hi, I'm trying to compile Monero from source in Ubuntu 20.04, but I got this: " Submodule 'external/miniupnp' is not up-to-date.", and after typing "git submodule update --init --force", I got this: "fatal: remote error: upload-pack: not our ref xxxxxxxxxxxxxxx"

Is there any workaround? Thanks in advance.
Cheers.