GoAffPro provides you with the option to disable the commission for purchases made using store credits.
To disable commission on purchases made using store credits, go to the Commission Modifiers section in the Commissions tab of the GoAffPro admin panel.
Here, click on Add new modifier.
Now, select the "Payment gateway matches" rule.
After this, set the "matches" value to Store Credits.
Now, set the "adjust commission by" percentage to -100%.
Finally, click on Add Modifier.
The newly set commission modifier will prevent any commission from being calculated on purchases made using store credits.