Could I have the link to allow me to sign in/ register in the Messaging Assistant Web Tool?
This doesn't belong in the NAC (Network Access Control) community.
It sounds like you're an end user, reach out to your IT department for this, if you don't have PCA enabled, they need to enable it and provide you with the URL you need to use to access it.
If it has already been enabled, it would be accessible via https://<ip address of unity>/ciscopca but to Jaime's point, it needs to be enabled and granted to end users via class of service. Take care.
Find answers to your questions by entering keywords or phrases in the Search bar above. New here? Use these resources to familiarize yourself with the community: