Then as for why you are getting that error, it's likely the personal access key you are using to authenticate with your CLI tools does not have the serverless functions scope. You'll need to go in to your account and make sure it has that permission checked. View your personal access key permissions What is a personal access key?
Additionally the serverless functions permission, is only available in accounts that have access to serverless functions. That means CMS Hub Enterprise or developer sandbox accounts.
Sorry for delayed response! I noticed you also asked this question another thread ( I will answer there as well for anyone searching and comes across that post )
At this time, we do not have a good solution for limiting the access. It has been mentioned several times and we are investigating so stay tuned.