Trying to understand variable configuration #1

Hi, here's a snippet of my implementation of this action:
- name: repo-sync
uses: wei/git-sync@v1
env:
SOURCE_REPO: "[email protected]:hopeonesource/hopeonesource.org.git"
SOURCE_BRANCH: ${ GITHUB_REF:11 }
DESTINATION_REPO: "codeserver.dev.[redacted]@codeserver.dev.[redacted].drush.in:2222/~/repository.git"
DESTINATION_BRANCH: ${ GITHUB_REF:11 }
SSH_PRIVATE_KEY: ${{ secrets.SSH_PRIVATE_KEY_PANTHEON_REMOTE }}
with:
args: $SOURCE_REPO $SOURCE_BRANCH $DESTINATION_REPO $DESTINATION_BRANCH

The secret exists, however I am getting both a Permission Denied (public key) message as well as the following:

SOURCE=[email protected]:repo/repo.git:${
DESTINATION=[email protected]:GITHUB_REF:11.git:}
Warning: Permanently added 'github.com,140.82.114.4' (RSA) to the list of known hosts.
[email protected]: Permission denied (publickey).
fatal: Could not read from remote repository.

Please make sure you have the correct access rights
and the repository exists.
error: src refspec ${ does not match any
error: failed to push some refs to '[email protected]:GITHUB_REF:11.git'
##[error]Docker run failed with exit code 1

What am I doing wrong? It's tough to find documentation on how env vars are supposed to be referenced.