The mobile secondary card sends a text message saying that it is in arrears.

If it is arrears, it means that the balance you inquired is "account balance" instead of "current available balance of account", and "current available balance of account" is the real available balance, which means that your current available balance has no balance and is in arrears.

1. Current available balance of the account: the total balance at the beginning of the month after deducting the current month's consumption and related arrears is the balance of telephone charges that you can really use. Only look at "Current Available Balance of Account";

2. Account balance: refers to the amount left in the account at the beginning of the month after the account was closed last month (including available advance deposit, available grant, frozen advance deposit and frozen grant), because it was not consumed in the current month. For example, for users who enjoy the monthly phone bill, the unused gift fee will be deposited into the account as a frozen total amount, forming an account balance, but this amount cannot be used immediately and is not really available.