Connecting a bank directly to invoices isn't possible in QuickBooks Sole Trader, shaundix44.
The bank connection is designed to automatically download transactions for you to review, not to directly process a customer's payment. However, if you are referring to making your bank account appear as a deposit option when recording an invoice payment, you must first connect the bank through the Bank transactions panel.

Once connected, your bank will be available in the dropdown menu for you to select when you record a payment, ensuring that the funds are correctly deposited into the right account within your books.

However, if you're referring to something else, please share a few more details. Knowing what you were trying to accomplish or if you saw a specific error message will help me get you a more precise answer.
The entire QuickBooks and other members of the forum are always here if you need more help from us.