How to follow another user from another instance of Plume or WriteFreely

I haven't been able to do it the correct way... which is find a user at their instance, click the follow button, then type in your username and instance and have it follow. I always get this error:

Error: Invalid URI used for redirect.
Warning: Responding with 500 Internal Server Error catcher.

Instead, I have found, from reading the Plume documentation here, how to do it an alternative way that works.

Try typing this into your web browser:

Where is your instance and user@other.instance is the username and server name of user at the other instance, Plume or WriteFreely, who(m) you'd like to follow.