Missing customer in the Customer drop-down

Hello, @terenceteo. Let's ensure you'll able to find your customer from the drop-down menu in QuickBooks Online (QBO). 
 

Before anything, let's go to the Customer section to verify is your Customers is still active. Here's how:

1. Navigate to Sales from the menu.
2. Go to the Customers section
3. From the Gear icon near the Action column, tick the include inactive box.
4. Find your customer.

If your customer is still missing, let's troubleshoot your web browser to determine what's causing this issue. 
 

Here's how:
 

1. Relaunch your browser.
2. Open your QBO account using a private browser.
3. Clear your cache.
4. Add Intuit as a trusted site. 

In addition, check this article for more information on efficiently handling your customers in QBO:  Add and manage customers in QuickBooks Online.
 

If you have further questions on finding your customer from the list or any other concerns inside QBO, please let us know. We're always here to help. Have a good one.