Member Formula - Net Calc

The way Calculate works, it's meant to create records in the database that will contain the results of a calculation. To do that, you always have to specify a set of destination coordinates for the records you will be creating; that has to be on the left hand side of the assignment operator (=). So in your case, the formula should probably look something like this:

api.data.calculate("A#Interest_Expense_Net:F#Cash_Input = A#WC_Interest_Income_ThirdParty:F#Cash_Input - A#WC_Interest_Expense_ThirdParty:F#Cash_Input")

 You should probably review the parts of the Design & Reference Guide that deal with Stored Calculations and Member Formulas. I would also recommend the OneStream Finance Rules and Calculation Handbook, available at online bookstores (Amazon etc).