Can stack with free shipping codes and works with this Zip deal https://www.cheapies.nz/node/25552
Update: Use "1-dollar-app" for $1 delivery. Might have to use the Warehouse app.
If you haven't signed up for giveit, do so in the app for another $5 credit.
So $15 off + $20 zip20 + $5 giveit would give $40 off $100 in total.