Can't add repo

[timothybuchanan]

Trying to install matrix software on Rpi3 running Buster OS. Your directions for setup are not working.
curl https://apt.matrix.one/doc/apt-key.gpg | sudo apt-key add - gives this error:

curl failed to verify the legitimacy of the server and therefore could not establish a secure connection to it. How to fix this?

[copitz]

Use curl with -L (see #56)