Nissan Finance (US) is denying access to your account.

Garymal

I'm getting the message when i"m try to connect nIssan Finance.

Nissan Finance (US) is denying access to your account.

Please visit the Nissan Finance (US) web site to see what’s going on.

Care Code: FDP-109

UKR

Looks like they don't want "third-party aggregators" like Quicken, Intuit, etc. to access their computer systems, "for reasons of improved security from hackers".

Instead of attempting to activate any loan or mortgage accounts for downloading, I would just simply set them up as "offline" (manual) loan accounts with a Scheduled Reminder to record the monthly payment from your checking account.
(Not discussing LOC or HELOC accounts here. They should be set up as offline credit card accounts)

At least in Quicken for Windows, an online-connected loan or mortgage account does NOT have a transaction register. All data shown in the account come from whatever information the bank downloads to you ... if this process works at all.

As a result of being connected, the scheduled payment transaction reminder cannot transfer the amount of principal paid into the (non existent) account register and must use a category, usually something like Loan:Principal, instead. The category name seems to vary with the Loan Type you selected when creating the loan account in Quicken.

Effective with Quicken Windows 2018 and newer
you should be able to deactivate an online-connected loan account and regain full control over your transaction register. And you should also review the Scheduled Reminder (or Memorized Payee List entry) associated with the monthly loan payments to ensure they now transfer Principal to the loan account register and not to a Category.

If you're a Q Mac user, you should be able to do something similar about setting up and maintaining an offline mortgage account together with a correctly calculated Scheduled Transaction Reminder for the monthly payments from your checking account.

P.S.: Quicken may not be able to calculate principal and interest to the penny for car loans, because the bank calculates car loans similar to credit cards and not like mortgage accounts with a fixed payment schedule.
That means, you will have to edit each monthly payment transaction's principal and interest amount based on the numbers shown in your monthly statement from Nissan.