This is because your friend invited you using an email address different than the contact email address used for your Joomeo account. If you have access to this Joomeo space you can add it by clicking on "+Add" on the "My network" panel. You have two choices:
After entering one of these 2 pieces of information, enter your user name and your password. You may access this space after it is added to your network. (Attention, user name and password are different from the ones you use to access your Joomeo space. Use the user name and password that your contact sent to you).
Maybe now is a good time to take a few minutes to see the main functions offered by Joomeo. We have prepared a few tutorials and videos on this topic for you: