You receive an error when cloning a submodule or an additional private repo dependency.
Example error when cloning a submodule:
remote: HTTP Basic: Access denied fatal: Authentication failed for 'https://address.com/owner/repository-name.git/'
Example error when cloning a repository from Xcode:
xcodebuild: error: Could not resolve package dependencies: Authentication failed because no credentials were provided.
In order for the SSH keys to work, the format of the URL for the dependency has to be the following:
Make sure you are following this format wherever you reference the address of a repo dependency. You should also use this format for the Repository URL field under the "Settings" tabs for the app.
You should not use `https://` based URLs for the app or for any dependencies needed.