Just found it on the front page on Groupon's website!
Free Shipping on Amcal.com (Don’t pay $7.50) - No Min Spend.
How to Redeem:
• Amcal code is valid until: 30 Apr 2017 (11.59PM AEST).
1) Claim your free shipping for Amcal on Groupon
2) Use shipping code at online at: https://www.amcal.com.au/
• Shipping information page: https://www.amcal.com.au/shippinganddeliveryfees
Limit of 10 vouchers per person.
Max 1 voucher per transaction.
Valid for online redemption only.
Valid for shipping within Australia only.