You can add as many Short.io users as needed to a team following the procedure below:
Sign in to your Short.io account.
Navigate to the Settings -> Teams menu:
Click on Add new member:
In the next screen provide the following information:
enter the Email Address of the member
select the member's Role (more information on roles is available here)
in case you select User for role, you can enable the Link-level permissions option (allowing the team member to see only short links that they created)
You can add as many members as needed by clicking on More members and when all the settings are completed, click on Add (<number>) new member(s) to confirm.
The new members are displayed and an invitation is sent to each of them with a sign-in link to Short.io.