What does "Pending" mean in the user's status section?

The "pending" status indicates that the user hasn't verified their email yet.

When a user is added, a verification email is sent to them which requires the user to click the link within before the link expires. If the link has expired, a new email should be sent to them.

In order to resend a verification email, you can navigate to Settings > User Management, click the 3-dot icon for the user in question, then select "Resend Invite".

Note - the user will not be active and will not be allowed to perform any operations until they verify their email. However, the user will take a user seat out of your allotted quota even when their status is pending. 

Please note that once in a while, a legitimate invitation email can be routed to your spam folder. If you are not receiving an invitation, please check your spam folder.