Within Teamwork.com, you can upgrade an existing contact to a standard user so they can log in and be assigned tasks.
Contacts are used to store details for reference and cannot log in to your site to interact with projects.
To view the People area, click the More option in the main navigation menu on the left of your site and select People.
In the People area, select the People tab from the horizontal menu to view and manage your users.
From the list of people on your site, click the name of contact you want to upgrade to view their profile.
In the top right of their profile, click the options button (three dots) and select Upgrade to Standard Account from the dropdown menu.
You will be asked to confirm if you want to upgrade the contact to allow them to log in.
Once you have confirmed, you will be prompted to send an invite email to the new user. You can do this later if you wish by clicking No, Thanks.
Whether you choose to send an email or not, the contact will be upgraded to a standard user.
For more information, see: Downgrading a User to a Contact