Can we Default the Category based on Helpdesk Channel?

Summary:

We have enabled the Email channel for creation of helpdesk ticket and Category is a mandatory field for us to create a SR hence we want to understand if its possible to default the category if the channel is Email.

Can we use a groovy for this. If yes, can we please have the sample Script.

Note: We tried this Groovy —— if (ChannelTypeCd =='ORA_SVC_WEB')
setAttribute('CategoryName','Drinking water') but system is throwing below error while clicking on create SR button.

"Exception in expression "oracle.apps.crm.service.svcMgmt.srMgmt.model.entity.ServiceRequestEO" trigger "Default_category" : oracle.jbo.ReadOnlyAttrException Attribute CategoryName in view object ServiceRequest cannot be set.