Hey there, @Gakasuki! Let me share with you some insights on what might be causing the red alert that's been popping up when you try to reconcile your bank in QuickBooks Online (QBO).
Initially, when you want to modify the date of a statement transaction that you have already downloaded successfully, you must first categorise, add, and match bank transactions. QuickBooks will search for and attempt to match your newly downloaded transactions with existing ones once you connect your bank or download your transactions. If it is unable to find a match, it will create a new transaction record for you, which you can either approve or reject.
I'll be adding this article for future reference for the detailed instructions on how to categorise and match bank transactions in QuickBooks Online.
Additionally, you can check out these articles to get more insights and information on reconciliation issue-related topics:
If you have any questions about other processes in QuickBooks Online, please don't hesitate to ask me in the comments below. Have a fantastic day!