Hello @IHwang
Thank you for reaching out on the community and telling us about your issue. I do apologize for the issues you're having. One thing we could try is trying to force delete that transactions to see if you're able to continue with re-enabling check pay and quick pay. The article to do so can be found down below.
https://www.quicken.com/support/cannot-delete-online-payment-or-payee
Try these steps out to delete the payment and see if you're able to get it to set up again properly. Also if there are any other issues please let us know and we'll see what we can do next.
Thanks,
Quicken Francisco