I too have tried to get the Citi Card from Costco to work again. This one worked for me today so I figured I would share it.
In the Account List, I went to Costco Visa - Citi, clicked Edit, and deactivated the Online Service. Saved and exited the Account List leaving the account.
Clicked on File, New Quicken File, New Quicken Account.
Did a search for Citi.
Noticed that "Citi Cards" had the same/similar website as "Citibank, and Costco Anywhere Visa Card by Citi"
The big BUT. When I click under Best Results - Citi Cards, I had the option to pick Advanced Options.
After click Advanced Options I got:
And picked Direct Connect. Next.
Got a suggestion to go to citi.com/datamanagement. See above. So I logged in to citi.com/datamanagement
I logged in, and just followed the directions to Manage Your Desktop Apps / Add Access / Allow Access /Continue / Manage Your Desktop Apps – You’re Almost There! / Clock Time
While it was counting down I went back to my Quicken program and Clicked Try Again Now. Then Next.
And the Add Account Came UP!!!!
And I was able to link to existing account!!!
And it worked!