Call to create the salesforceobject Campaign failed! Object reference not set to an instance of an object in Salesforce marketing cloud

I recieve the following error

Call to create the salesforceobject Campaign failed! Object reference not set to an instance of an object

When i try to execute the following code

set @cost=FormatNumber(22,"D") set @EventID = CreateSalesforceObject('Campaign',20,'IsActive','True','Name','test544','Description','test','Type','HQEvent','Category__c','','StartDate','2020-02-03','EndDate','2020-02-03','Status','Draft','EventCapacity__c','1','LocationType__c','Store','LocationName__c','Delhi','StoreCode__c','607','Address1__c','Delhi','Address2__c','Delhi','ZipCode__c','600107','City__c','Delhi','State__c','chennai','Country__c','india','Brand__c','Intel','ActualCost',@cost)    Output(Concat('test',@cost))

The error occurs only when i add the field "Actual cost" its a decimal field in the campaign object, i tried with different formats but still same error.

Can any one help me why this particular field causes this error..