How to use Rollup Summary in a Formula Field?

How to use Rollup Summary in a Formula Field?

I created a Rollup Summary (Decimal) field in my module, and it shows values correctly.


When I try to reference it in a Formula Field 
(e.g. ${Deals.Partners_Requested} - ${Deals.Partners_Paid}),
I get the error that the field can’t be found.

Is it possible to use Rollup Summary fields inside Formula Fields in Zoho CRM?
If not, what’s the recommended workaround?

Thanks

    Nederlandse Hulpbronnen