If you have an active SMARTY SIM:
You just need an invite from the Group owner.
Once you receive an email with your invite, you'll need to respond to the invitation to join the Group. Simply follow the link in the email, this will take you to your dashboard.
Click “Respond to invitation”. Carefully read the terms and conditions before accepting the invitation.
Once you accept, both you and the Group owner will receive an email confirmation that you’ve joined the Group.
If you have a SMARTY SIM to hand, but haven't activated it yet:
Activate it first, then follow the steps above to join a Group through accepting an invitation from the owner.
If you don't have an active SMARTY SIM yet:
A Group owner can order a SIM for you directly from their account. They just need to follow the steps here on starting a Group by adding a new SIM.
Bear in mind you must be at least 13 years old - or have parent or legal guardian permission - to use SMARTY as a Group member.