My question involves collection proceedings in the State of: CA

I am being sued by a debt collection attorney.What proof do they need to receive a judgement?Do they need a cancelled check?I will send them a formal request for documents.They would not send the documents informally.Could this possibly mean they are fishing?Would the court consider this lawsuit frivilous if they dont show or have insufficient proof?Please be as thorough as possible.I really appreciate your help.Thanks.