Failed to download public key


I'm trying to install OpenWrt on an old TP-Link device. I am following the instructions on

There it tells me to 'Verify the downloaded firmware file'. The instructions link to the page with info on how to verify the download:

It mentions the script, which seems very convenient. The script can't complete, however, with the default value:

Keyserver to use? [hkp://] > 
gpg: opvragen vanaf sleutelserver is mislukt: No name
Failed to download public key.
Cleaning up.

After some online searching I found this on GitHub:

The sks-keyservers are broken, its not recommended to use them anymore.

In this thread there are alternatives.

Using hkp:// the script succeeds.

It'd be helpful for beginners like me if the keyserver URL is updated.