Good day, Lhorie27!

Let me further assist you in handling your client's transactions.

When you upload a CSV file, you can match the uploaded entries to the existing transactions in QuickBooks Online and this won't cause any duplicate. This is another way of bringing in the bank transactions aside from linking the bank account.

For the detailed steps, you can follow the instructions shared by my colleague or check this article: Manually upload transactions into QuickBooks Online.

Also, I added this link to learn more about what to do with the imported bank transactions: Categorize and match online bank transactions in QuickBooks Online.

Keep on posting here if you need our help in handling bank transactions. Take care always!