Hi, if a parent is creating an account, the account creation screen includes a box for the pairing code. So I dont think they can create their account without completing the all the info (they can't create the account without the pairing code). See this Canvas Guide
Do you actually see the Parent's account in Canvas? If you don't see their account in your instance, I suggest they try to create their account again. Although there are Canvas guides (listed below), we created our own guides for our district.
Did the parent create the account in the right domain? (for example, the Find Institution screen says "What's your School's Name" but each of our schools does not have a separate domain (separate URL). We use our District's Name.