Trouble activating account on carthagenet

I’m playing around with carthagenet, but I’m having trouble activating an account with the .json file I got from https://faucet.tzalpha.net/

I’m using the docker script for carthagenet and I’m trying to activate an account with:

./carthagenet.sh client -A rpctest.tzbeta.net -P 443 -S activate account bob with "container:xxxXXXXXxxxxx.json"

but I get the error:

Error: Invalid activation. The public key xxxXXXXXxxxxx does not match any commitment.

Any idea what I’m doing wrong?