I can share some insights about how bank transactions are downloaded into QuickBooks Online.
If you set your account for online banking to download transactions, the system will automatically put them on the Banking page for review. If you want to include them in the customer's profile, add them as Sales Receipts. Other transaction types will not post to the customer profile.
Here's how to add customer transactions:
Go to the Banking menu from the left toolbar.
Select the bank account you want to review, then click on the transaction.
Choose Categorise, then pick Sales receipt for the Transaction Type.
Add the customer name, and fill in the Tax field.
Once done, press Add.
For other resources on how to manage your bank account and customers, see the following links: