Hi there,
The enrolment process is designed to work only with the auto-configured TLS setup that one gets with Elasticsearch 8.0.
You could theoretically alter your existing configuration so that enrollment works for you too but we don’t have any documentation around it and it’s probably going to be more work that adding a node with TLS using the documentation you have already followed.
The error message that you got in this case is misleading and we’ll look into making it clearer, thanks for your feedback !