previewPendingUsageInputs API is used to preview the rating amount of usage inputs without altering the Billing Schedules, Usage Schedules, and Usage Inputs. You can rate a maximum of 2000 Usage Inputs at a time.

The API accepts a set of Usage Input IDs as input. It validates the number of Usage Inputs to process. If the number of Usage Input Ids entered is less than 2000, it returns a map containing the rating amount for each Usage Input ID. If the number of Usage Input IDs given is more than 2000, Billing Management system throws an error.

Set<ID> usageInputIDs = new Set<ID>();
Map<ID, Apttus_Billing__UsageInput__c> mapRatedUsageInputs = Apttus_Billing.BillingService.previewPendingUsageInputs(usageInputIDs);
for(Apttus_Billing__UsageInput__c usageInput : mapRatedUsageInputs.values()) {
                //Use usageInput.Apttus_Billing__RatedAmount__c
}