If you have Credit Invoices enabled:
- Download the Invoices - Summary export (Invoice Type: Credit, Invoice Status: Open, Time Range: All Time) and then use the "Invoice_balance" column to calculate the total unused credit amount for each credit invoice in your site dating back to when you first enabled Credit Invoices.
If you DON'T have Credit Invoices enabled:
- Download the Adjustments export (Check the box for "Include uninvoiced adjustments", Time Range: All Time)
- Use the "adjustment_type" column to remove all charges.
- Use the "adjustment_status" column to remove all invoiced credits.
- Use the "adjustment_total" column to calculate the total of unused credits on your site.