As you have asked about the steps for the credit card bill payment of the Citibank at AXS stations, I am giving you some information about it, check below for the details

Make use of the wide AXS network island-wide to pay your dues and bills or transfer funds.

D-Pay is a new direct payment environment on AXS Stations that allows you to make payment securely using your Citibank ATM/ Debit Platinum Card.
The new D-Pay enabled AXS Stations have a prominent red frame sticker at the touch screen, keyboard and on the pin pad.
There is also a black colored front slot sticker that shows the participating banks.

Now you can pay your bills at D-Pay enabled AXS Stations using your Citibank ATM/ Debit Platinum Card at no transaction cost.
Credit Card, Telecommunication bills
Income tax, insurance premium and loans payment
LTA, carpark and traffic police fines
Top up of M1, SingTel and StarHub pre-paid card

Step-by-step Guide:

Follow the on-screen instructions on the D-Pay enabled AXS Stations to select the billing organization; billing account and amount
Insert your ATM/Debit Card into the card reader when prompted
Select Account Type
Key in your 6-digit PIN
Upon successful transaction, collect receipt from the receipt outlet
Retrieve your card after transaction