To setup your auto top up, click edit auto top up
...
Select “Enable auto top up”
“Minimum account balance” - amount to be set to your desired amount,
“Top up amount”- take into account the monthly plan charge as well as any additional charges on the account such as additional call packs phone numbers etc.
Select “Payment Method” - this will then authrise your chose of payment automatically each time the balance is below the “Minimum amount”
Press “Save”
...