If you are subscribed to the Business-plan, you can collaborate with others by adding team seats to your subscription. This way, you can invite users to your teams and assign them to projects to work together.
How to add team seat
On your profile menu, you go to Billing;
You write down the number of seats you want to add and click Subscribe
After you are done with your payment, your team users can use Heyweek.
NOTE: Added users will have access to the projects you have assigned them to. They can not create their own projects and clients unless they have an active Business plan subscription.