CardUp is a service that allows you to use credit cards to pay for transactions which would normally not accept credit cards, like home loan payments, season parking, condo MCST fees, tuition fee payments (protip: SMU takes Apple Pay!), insurance, rent and income tax payments. This allows you to earn credit card rewards points, in exchange for paying a 2.6% admin fee.ย 
CardUp launched a referral program back in March 2017 which enabled existing users to gift $20 in CardUp credit to new users (you can use my code MILELION or any of the codes in the comments section here. Pleaseย do not post referral codes in the comments section of this article), while receiving $20 credit of their own when the new user made his/her first payment.ย At a 2.6% admin fee, that $20 of credit would be enough to cover the fees incurred on a $770 maximum value transaction.ย
CardUp sent out an eDM yesterday announcing some changes to the referral program. From 12 June 2018, newly-issued referral codes will require a minimum spend of $1,000. That is, whoever you refer needs to spend a minimum of $1,000 to get $20 off the CardUp fee, and whatever referral credit you get can only be spent with a minimum transaction of $1,000.
Assuming you just hit the minimum transaction figure, you’re paying $6 (2.6% * $1,000- $20) worth of fees.ย There’s a maximum of 20 successful referrals per account, and the referral program has since expanded to include Businesses as well with a $100 referral credit (valid till 31 Aug 2018).
The good news is that any Cardup credits accrued prior to 12 June 2018 can still be used with no minimum threshold.ย That’s fair enough, I suppose, so existing users with referral credits shouldn’t feel hard done.
It appears that 10X opportunities with CardUp are dead for now, so your best bet is a general spending card like the UOB PRVI Miles, which allows you to buy miles at ~1.81-1.85 cents each (because of UOB’s practice of rounding down, the actual price depends on the total amount you pay including fees). Should you be buying miles at 1.81 cents each? As with all things, it depends on what your intended use is. Be sure to check out this article on the different ways of buying miles in Singapore and see what makes sense for you.
More FAQs about CardUp referral credits are answered here.
In the past, for CardUp income tax payments, used to be case whereby if one pays sufficiently early before GIRO date, the eventual GIRO deduction will be reduced accordingly. Now for past two months, this was no longer the case. After paying via CardUp, IRAS still GIRO deduct the original amount. Saving grace is that the outstanding tax amount was “double reduced” accordingly. In effect, one is making early payment, as opposed to substituting the GIRO payment. I wonder if the now different treatment is because of provisional GIRO plan? Any one got recent experience to share?
It seems the plausible explanation is that the ad-hoc income tax payments do not substitute (i.e. reduce) the GIRO deductions under a provisional plan, as opposed to when under a finalised GIRO instalment plan. The monthly deductions will be re-calculated accordingly once the tax bill is finalised (i.e. NOA).