Which IP should be used for a DO's managed database MySQL user on a private network?

Question

I have a droplet and a managed database both in the same region and with Private Network turned on.

I want to create a database user but I'm not sure which IP should I be using for this new user, should it be the droplet's public IP or the private IP?

CREATE USER 'user'@HOST IDENTIFIED WITH mysql_native_password BY 'password';

Which IP should I have instead of HOST?