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
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.