I am having trouble creating logins from client invitation

Hi,

My client has sent me an invite link to join as a content editor so I can start managing the site. I have received the email but when I click to Join now. It opens a new tab with the client’s website and a pop-up from the bottom of the screen comes saying to join.

When I entered my Name and password (The email is autofilled because it was the invited email by the client) It showed an error saying:

The request is malformed: No user was found with this email.

But the thing is I already have a Webflow account.

Please guide.
Thanks
-M