Thanks for providing further details, Hannah. Here's the information you need to import your bank transactions.
Since you've verified your format is correct, the next thing you'll have to ensure is the accuracy of your mapping. The red exclamation (!) symbol in a circle indicates that a date is needed for the section that's missing this information.
Once the required data is entered, start re-uploading your CSV file. Please see the For customers using QuickBooks Online drop-down section for the step-by-step guide: Manually upload transactions into QuickBooks.
Otherwise, I recommend contacting our Support team to report if the issue continues. Here's how:
Moreover, I encourage you to reconcile your accounts regularly (monthly). Doing so will let you track your finances and manage them accordingly.
Please don't hesitate to comment below if you have other banking concerns or inquiries about managing your transactions in QuickBooks. I'll be sure to get back to you. Take care always.