How do I claim the free monthly challenge accounts?

To reward your hard work, you can claim free accounts at the following milestones:

50 referrals/ month: 25k challenge account with full add-ons 

100 referrals/ month: 50k challenge account with full add-ons

200 referrals/ month: 200k challenge account with full add-ons

400 referrals/ month: 400k challenge account with full add-ons

Resets at the 1st of each month.