Invite a collaborator – whether they have an existing account, or not.
Go to your project dashboard.
Select the project you want to share with a collaborator.
In the right-side menu, click on the sharing tab.
Enter in your collaborator's email address. If they already have a First Draft Pro account, you'll be able to select their account from a prompt.
Click "send invitation".
Your collaborator will receive an email inviting them to join your project. Once they accept the invitation, they'll be able to work with you on that project.
❓ Read more about collaborator permissions.