I finally got a resolution to this after 3 hours in a phone loop between TurboTax and IDnotify support.
For reference, here is the page stating that a secondary filer is covered under MAX benefits when filing jointly: https://ttlc.intuit.com/community/choosing-a-product/help/what-is-max/00/26700
When we enrolled in MAX benefits during/before filing, I received an enrollment email to create an account, however no instructions were provided on how to create an account for the secondary filer.
Do not bother calling IDnotify support ([phone number removed]), they insist that there is nothing they can do regarding enrollments and that is completely under TurboTax control, which is true.
Eventually TurboTax support [phone number removed]) was able to provide an enrollment link for IDnotify, which creates an IDnotify account specifically for TurboTax customers. NOTE: you must not be currently logged into any other TurboTax or IDnotify sessionsthis link to work (Try private/incognito browser session, if necessary) . TurboTax will need to provide you with the unique PIN Code: https://portal.idnotify.com/enrollment/2?RTN=90000121
Best of Luck,
