In order to invite additional members to your organization, follow these steps:
Click on the 'Settings' button at the bottom of the left vertical menu and then on '+ invite members'. This will take you immediately to the Invite Members screen
Type the name and email of the person you would like to invite and specify the role for the invited user. Use admin in case you would like to allow the invited user to add/remove users and delete environments that were not created by them. Invitation links expire after 30 days.
Newly invited users are added to the organization members list with an ‘Invitation Sent’ indication until they accept the invitation by following the invitation link that was sent to their email address. As long as the invited users haven’t accepted their invite, you can either cancel the pending invitation or copy the invitation link in order to manually send it to them by a messaging app of your choice.