Only team admins can invite people, and the organization owner is admin of each team they create.
Open Organizations in the sidebar and click Manage next to the team to open its Members page.
Click Invite Member, enter the email address and choose Member or Admin.
The invitee clicks Accept Invite in the email, then signs in or chooses Create Account with the invited address.
Invites expire after 72 hours; after that, just invite the address again. While an invitation is still valid, inviting the same address returns "This email is already invited or a member", so first click Cancel next to it under Pending invitations on the Members page.
Member runs models, creates projects and chats with team agents. Admin can also edit Team Settings, manage members, roles and spend limits, transfer credit and redeem coupons for the team, and edit, transfer or remove the team's projects and see their API Secret. A Member who creates a team project sees its API Secret only once, in the window that opens after Create Project, so copy it then. Everyone in the team sees all members and their spending, and team runs charge the team wallet.
Details: How do organizations and teams work? and Managing Teams.