Referral codes are earned based on platform activity. You will receive your first referral code once you reach $1M in trading volume.
For every additional $1M in trading and/or referral volume generated, you will unlock one additional referral slot.
You can find your referral link and progress in the Referral tab.
Alternatively you can apply for Variational Affiliate status to receive an increase in referral codes plus a number of other benefits.