I got confirmation that it had been attached on Tuesday, so not sure if it was the Faxed or Web Form document that got attached (it doesn't matter anyways since it is the same document). I also mailed it, but it had not gotten to IRCC yet when I got confirmation that it had been attached. So I know it was not the one I sent via mail.
The agent that told me to send it via fax said I should include a letter of explanation. In the letter I included the Application ID, Name, UCI, Country of Birth, Country of Residence, Date of Birth, Email Address, Address, and telephone number for both the sponsor and principal applicant.
Hope this helps.