What is Credit?
Credit is an amount paid in advance to Billplz for fees deduction, i.e.: Membership Fee (Standard or Enterprise Plan), FPX Transaction Fee (Basic Plan; RM1.50 / Standard Plan; RM1.00 / Enterprise Plan; RM0.50 or RM0.70), Activation fee (for card/e-wallet), Payout Fee (incurred per payment disbursement requested) and also RM0.30 per SMS request fee.
If you are simulating payment on staging, you can choose either to reload credit on leave the credit as is. Reloading credit in staging doesn't involve real payment. You may refer to How to reload credit for tutorials.