Quicken 8.3.2,, macOS 15.6.1.
I receive monthly payments from a borrower that get deposited directly into a checking account. In Quicken Mac I set the category to "Transfer" and the transfer-to account as the loan account. This worked just fine for several years. I just noticed that, starting with transfers in October 2024, the transfers were marked with the white arrow inside a red circle meaning "invalid transfer." The invalid transfers were identical to the dozens of previous transfers. None of the "invalid transfer" transactions in the checking account appeared in the transfer-to account.
To fix the problem, I had to edit each "invalid transfer" transaction separately. I double-clicked the transaction in the checking account to edit it and changed the transfer-to account to another account and saved the change (it didn't seem to matter which different transfer-to account I picked). Note that I DID NOT GET A CONFIRMATION pop-up when saving this change. I then double-clicked the transaction in the checking account again to edit it and changed the transfer-to account back to the loan account. This time I DID get a confirmation pop-up. Once confirmed, the "invalid transfer" icon disappeared and the transaction appeared in the loan account as intended.
I don't know why this "invalid transfer" started happening but that is how I fixed it; I did not have to delete any transaction. The "invalid transfer" error does not appear on any other deposits that have a transfer as the category.
