Below are the 3 cases which could be causing the problem

You are already registered for Chatwork

If your account registration is already complete, you will not be able to access the URL.

Please login from blow to use Chatwork:
https://www.chatwork.com/

URL in your email contains a line break

The URL may contain a line break.
Please try copying & pasting the URL to your browser directly. 

You are trying to access the URL for a different user

Registration URL is unique per registered user.
You will not be able to use different user’s registration URL.