How to represent a Rule which returns a value, in a string in another expression

[arrafeeahsan]

{
"Name": "RemainingCount",
"Expression": "ActiveMemberInGroup - DefaultActiveMemberNumberPerGroup"
},
{
"Name": "Message",
"Expression": "RemainingCount > 0 ? "Maximum number are {RemainingCount} " : "Maximum Number are 0!" "
}

[bmasotta-lcg]

You can use an OnSuccess Action of the type (Name) OutputExpression and then specify your expression in the context Expression
You will be able to see the result in the RuleResultTree.ActionResult field

 "Actions": {
         "OnSuccess": {
           "Name": "OutputExpression",
           "Context": {
             "Expression": "CustomType.GenerateMessage(GlobalParamSomething, RuleParamOther)"
           }
         },
         "OnFailure": {
         }
}