In Bank transactions tab, I am trying to select Payee and Category. I added some customers and categories manually but it's never shown up. How I can do this?

I'm at your service to help you overcome this banking challenge involving the selection of Payee and Category, Yuya.

Typically, once you've added a customer and categories into the system and saved them, they will automatically appear on the selection list. 

However, what you encountered did not occur in the manner you mentioned. Consider switching to another supported browser to confirm whether the added customers and categories will be visible on the dropdown list. 

If they are still not visible, kindly contact our customer care support so they can pull up your account and provide you with more troubleshooting steps to fix this issue.

Here's how:

1. Go to the Help menu at the upper right.
2. Click the Search tab.
3. Press Contact Us at the bottom part. 
4. Enter your concern in the What can we help you with? box.
5. Click Continue.
6. Select Chat with us or Have us call you.

In addition, you can take advantage of the bank rules feature to automatically classify your banking transactions. Refer to this article for more details: Set up bank rules to categorise online banking transactions in QuickBooks Online.

Please let me know if you have other questions regarding managing bank transactions or other relevant issues in QBO. I am always available to assist.