Basically $20 free credit and then you get half of your fare as a discount off your subsequent next fare. Similar to this deal.
T&Cs
The 25% rebate is applied as credit to your GoCatch account for all rides until 11:59pm 30 June 2018. This Rebate Offer is valid for on-demand trips and Advance Bookings in a GoCatch Economy, Taxi, Maxi or Premium excluding payments outside of the GoCatch App including, but not limited to, Taxi jobs with external payments, cash, EFTPOS, or Cabcharge. The 25% rebate is calculated from the paid fare value of the trip, less credit used on the trip, tips, tolls, levies, and surcharges. The trip must occur between 7:30am Tuesday 29 May 2018 and 11:59pm Saturday 30 June 2018 to be eligible for the 25% credit rebate. Trips occurring outside this period will not be eligible. Any promotional or voucher credit applied to a trip will be deducted from the fare value when calculating the 50% rebate. This offer ends 11:59pm Saturday 30 June 2018.
$20 credit valid from 7:30am Tuesday 29 May 2018 until 11:59pm Saturday 30 June 2018. Credit can only be redeemed with on-demand trips and Advance Bookings in a GoCatch Economy, Taxi, Maxi or Premium excluding payments outside of the GoCatch App including, but not limited to, Taxi jobs with external payments, cash, EFTPOS, or Cabcharge. Passenger must have entered a Credit/Debit card, PayPal account, Android Pay account, or Apple Pay account as a saved payment method in the GoCatch app. If the total fare is greater than $20, the remaining balance will be charged to the nominated payment method. Any unused credit will be forfeited.
I tried to use gocatch with a previous $20 code but the app struggled to find drivers in suburban Belconnen. When it finally did they were 10-15 min away, one cancelled and one wouldn't move after like 5 min. So I used Ola instead