It is important that your representative has authorization with CRA. Currently the only way to get a business account authroized is to do it through the online portal at CRA called "My Busines Account"
Here is a video you should watch to setup your account. Once that is done, you can add us as your represenative.
https://www.canada.ca/en/revenue-agency/services/e-services/cra-login-services.html
