I agree with the output:
Please verify ... you have SSH forwarding set up correctly.
More info:
https://roots.io/trellis/docs/ssh-keys/#cloning-remote-repo-using-ssh-agent-forwarding
As the listed link mentions,
- ensure that your ssh key is added to your ssh agent
- list currently added keys:
ssh-add -l
- add keys:
ssh-add
- list currently added keys:
- and — since you’re on MacOS — ensure the key’s password is imported into your Keychain:
ssh-add -K
In addition, if you’re on MacOS Sierra, be sure your ssh agent isn’t “forgetting” your keys: