Go to Customer App > find the customer account > View > Payment:

You are able to see how much they are able to use:

• Usable credits: how much the account can spend this month. 
• Expecting invoice = unbilled amount: the usage amount for the current bill period = the amount that has not been billed/ invoiced yet. Depend on how you are setting up the invoice, the unbilled amount is determined differently.

• Current balance: allthe amount the customer needs to settle, including the billed and unbilled amount.
  • If the current balance is DR, it means the customer has not paid for them yet. 
  • If the current balance is CR, it means the customer has already overpaid.
    • Current balance = Expecting Invoice + Amount Due
      • Example 1: Current balance = (-1610.61) + (-0.20544) = (-1610.81544) SGD
      • Example 2: Current balance = 65.98 + (-0.000009) = 65.979991 SGD
• Credit limit: the maximum amount of money that you let the user borrow. Credit limit is applied on the unbilled amount and is reset every month for postpaid users.
• Reserved credits: are caused by an ongoing transaction. If the transaction is successful, Reserved credits will be deducted; otherwise, they will be returned to the Usable credits.
• Amount Due = billed amount: the sum of all costs they have been invoiced for, minus any payments that have been applied to those costs.
  • If the amount due is DR, it means the user has not paid the invoice yet.
    • Maximum Expecting invoice = Credit Limit
    • Usable credits = credit limit + expecting invoice (unbilled amount) - reserved credits
      • Example:
        • Usable credits = 1000 + (-0.20544) - 0.01 = 999.78456 SGD
        • Maximum Expecting invoice = 1000 SGD
          
          
  • If the amount due is CR, it means they have already overpaid by that amount. The overpayment can be used to pay for subsequent invoices.
    • Maximum Expecting invoice = Amount Due + Credit Limit
    • Usable credits = Credit limit + Amount Due (billed amount) + Expecting Invoice (unbilled amount) - Reserved credits
      • Example: 
        • Usable credits = 100 + 65.98 + (-0.000009) - 0 = 165.979991 SGD
        • Maximum Expecting invoice= 165.98 SGD