Each account needs to be paid separately.

How to pay your own MBB card bills in M2U:

- click on your card details
- you should see Pay Now next to the statement balance, click that
- select your saving/current account to pay

u need to check are the principal and supplementary combine statement..
if combine statement, just paying to principal will do.
call CS to clarify this if you not sure is combine statement or sperate statement
you cannot pay supplementary card if it is combine statement..
only pay to principal will do

You can use Principal's account to pay for both.

For my case, my supp uses their own m2u to pay for their bills.
No problem at all.

Most importantly is, what is the error you encountered?
Insufficient funds? Pay more than statement balance?
Please bear in mind that the saving account has a threshold of minimum amount to be there, depending on which type of account, ranging from RM1 to RM250.

did you received your statement? I doubt you haven't receive the statement yet, hence just wait for the statement.
once received the statement, if it is combined, you will saw your supplementary card transaction amount will be combine to your main account. After that, just login to m2u to pay the main account's cc - statement amount before due date(statement date+20days).
the final statement amount which you saw in m2u on your main credit card account is the 1 combine both (main +sup) transactions.

then you can just pay to principal account..