If you are a person in charge of a vehicle carrying goods whose value exceeds the specified value, you need to carry certain prescribed documents with you, and it includes invoice and declaration. 

A proper entry must have been made in the books in respect of the goods being transported.

This is because proper officer has the power (authorized by the Centre or State) to intercept goods in transit.

On interception, the documents and goods can be inspected by the proper officer. If any person transports any goods or stores any such goods while in transit without the documents prescribed under the Act (i.e. invoice and a declaration) or supplies or stores any goods that have not been recorded in the books or accounts maintained by him, then such goods shall be liable for detention along with any vehicle on which they are being transported.

So you need to make sure you have the prescribed documents and a proper entry has been made in the books.