According to the regulations of the State Bank, TrueMoney don't support "Direct topup" for Not-identifed account.
Instruction identified account with Standard information: https://bit.ly/2tdPFGa
Please follow these steps below:
Step 1: Log into your account/ Choose Direct topup
Step 2: Input Phone Number and Select Amount
Step 3: Confirm payment
Note: Currently, the Direct topup feature for Viettel is not support. You can buy card mobile viettel by links: INSTRUCTION TO BUY EPIN
Payment limit: https://bit.ly/2IaCYQX