I saw this comment thread:
https://community.simplifimoney.com/discussion/5835/adding-teacher-retirement-system-of-texas-does-not-work
I did reach out to TRS and they said "TRS does not have affiliation with that company. The company could be blocking access because TRS is a government pension." (and obviously misunderstood that Quicken was blocking TRS instead of TRS blocking Quicken).
The error is CC-555 after entering the username and password (no MFA validation like the post above).
What are the next steps to fix this?