Canva allows you to stack up to 12 months of free Pro via referrals. After that, you need real paying referrals.
Some educational institutions offer Canva Pro subscriptions to their students and staff. Check with your school or university to see if they offer Canva Pro as part of their educational resources.
Canva Pro allows teams to collaborate. If a friend, colleague, or company has a Canva Teams subscription, they can invite you to their group.