When I attempt to add a trusted key by:

gpg --armor -- export ########

All is well and the key is output to the screen.

But, when I attempt the same procedure, using
the same ########, except to
add the key to the trusted keyring by:

gpg --armor --export ######## | apt-key add -

I get:

invalid packet
invalid keyring

What's wrong and how do I cure it, please ?

Thank you,
Courtney