The link above no longer works. I would like a referral, preferably before/on December 9, 2021.

The error received is:

This site can’t be reached

Check if there is a typo in refer.grubhub.com.
DNS_PROBE_FINISHED_NXDOMAIN

Edit 1: browsing the net, it seems the current referral offer is for $10 credit to both referrer and referree.
Edit 2: No longer need a referral.