The service to submit documents to the CRA that was introduced last year has changed. The expanded service allows you to submit certain documents, other than those in response to a request for documents with a case or reference number. To access the list of allowable submissions and to submit related documents, proceed as follows.
i) Select the client type and indicate if you have a case or reference number
ii) Provide the client's identification number (SIN, BN, etc.).
Click on Continue.
The page Submit documents - Upload file will display.
Attach the file(s) and click on Upload file.
Learn more About Represent a Client from the CRA's website