Mallzee no longer offers a referral credit scheme. Any credit you have earned by referring family and friends will expire on 31st December 2019.
Don't worry, if you still have time to spend your credit and enjoy free standard delivery. :)
Just remember that orders need to be £10 or above to get the credit applied.
You can see full t&c's here: https://mallzee.com/page/referral-scheme-t-cs