We have 3 Rollup Summary fields that provide a count of child records and fields with a particular status. We would like to add the values of these fields and use them in layout or business rules, but we get a syntax error whenever using them in a formula.
Is there a way to accomplish this?
Rollup Summary Fields are
universal, read-only fields
should not be used to build filter criteria for Formulas, Data Policies, Validations, Indexes or Searches
cannot be created based on a Rollup Summary Field
But in your case as you have roll up summary field for only count the child records with some condition so you can do it without using Rollup field. Do it in following way
Instead of Rollup Summary create a read only number field and default value should be 0.
On the creation of child record put a business rule to increase the number field by 1 and on deletion decrease the number field by 1
So it will act like a roll up summary field which will store the record count of child recods and you cant change it manually as it is a read only field
Now you can use this field in formula or actions.