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