If your balance in the transaction currency is insufficient, the system will automatically attempt to deduct from the next available currency based on the applicable deduction sequence. 

Currencies with insufficient or no available balance will be skipped. If your total available balance remains insufficient and Auto Transfer is unable to cover the shortfall, the transaction will be declined.

The deduction sequences are as follows:  
Spending Currency → MYR → USD → GBP → EUR → SGD → AUD → HKD → CNY → JPY

To resolve the issue, you may turn on your Auto Transfer.