Maybe less or nobody tried before. 1st the online rebate for OCBC 365 is not attractive after minus the cardup fee. 2nd the tnc exclude many items that cardup payment support. From OCBC 365 tnc:
Retail transactions are purchases for goods and services and exclude the following transactions:
(a) Payments made via telephone or mail order;
(b) Subscription and recurring payments;
(c) Payments to government institutions;
(d) Payments to financial institutions (including banks and brokerages);
(e) Payments to insurance companies; (f) Utility bill payments;
(g) Donations;
(h) Payment of funds to prepaid accounts and merchants who are categorised as "payment service providers";
(i) Payments to schools, hospitals, professional services providers and payments for parking lots
(j) Payments of membership fees to clubs and associations;
(k) Payments made via online banking;
(l) Any other transactions determined by OCBC from time to time.
So high chance OCBC will exclude cardup if the banker check what cardup payment categories.