How to provide an SSH certificate and private key to Aptible

I'm trying out a HIPAA-compliant PaaS, Aptible, by following their Django Quickstart Guide. I've used the aptible CLI to follow the Create an App and Provision a Database steps, but I'm running into trouble at Add a Dockerfile.

This step says to add a Dockerfile at the root of the repository, but no repository has been created yet by the previous steps. I assume I have to clone the repository using the Git remote link generated in 'Create an App'. However, if I do this (and ignore the warning about the authenticity of the host), I get a Please make sure you have the right access rights and the repository exists:

Kurts-MacBook-Pro:Scratch kurtpeek$ git clone git@beta.aptible.com:lucy/test_app.git
Cloning into 'test_app'...
The authenticity of host 'beta.aptible.com (52.21.95.179)' can't be established.
ECDSA key fingerprint is SHA256:FsLUs5U/cZ0nGgvy/OorvGSaLzvLRSAo4+xk6+jNg8k.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added 'beta.aptible.com,52.21.95.179' (ECDSA) to the list of known hosts.
Connection closed by 52.21.95.179 port 22
fatal: Could not read from remote repository.

Please make sure you have the correct access rights
and the repository exists.

Based on Aptible's FAQ, https://www.aptible.com/documentation/enclave/troubleshooting/permission-denied-git-push.html, I inferred that I hadn't yet registered my SSH Public Key with Enclave.

Indeed if I go to Aptible's Dashboard and click 'Certificates', I see that I don't have any yet. If I then click 'Upload Certificate' I get to the following menu:

This is probably quite a general SSH question, but I'm unsure how to proceed here. I've tried the ssh-keygen command as follows:

Kurts-MacBook-Pro:~ kurtpeek$ ssh-keygen -t rsa
Generating public/private rsa key pair.
Enter file in which to save the key (/Users/kurtpeek/.ssh/id_rsa): 
Enter passphrase (empty for no passphrase): 
Enter same passphrase again: 
Your identification has been saved in /Users/kurtpeek/.ssh/id_rsa.
Your public key has been saved in /Users/kurtpeek/.ssh/id_rsa.pub.

It would seem that the id_rsa thus generated corresponds to the Private Key requested. However, where can I find the (corresponding) Certificate?

(I perused https://support.ssh.com/manuals/server-admin/64/userauth-cert.html but couldn't find an answer).

It turns out that in order to follow the Django Quickstart Guide, it suffices to provide an SSH key (not a certificate). This can be entered by clicking your name in the upper right hand corner of the dashboard, selecting "SSH keys", and copy-pasting the contents of your ~/.ssh/id_rsa.pub in the form.