When running OSU the Discover Card account has been generating a CC-800 error since around the last update.
I've followed the "Fix It" instructions, which found the account, but only offered the "Don't add to Quicken" option. So, I manually deactivated the account and tried to add it again. I thought I was successful when it offered the option to link to the existing account. But on the next OSU it produced the same CC-800 error again.
I dread updates. Something always goes wrong.
Windows 11, Quicken Ver R54.16 Build 27.1.54.16