How to create customer account numbers in QuickBooks online?

Good day, jotabalba.

If you mean creating your customer's account number is saving it on your QuickBooks Online account, you can follow these steps:

1. From the Sales tab, select Customers.
2. Click your customer's name.
3. On the upper-right side, click Edit.
4. Go to the Payment and billing tab.
5. On the Preferred payment method field, select Credit Card.
6. Click the Enter credit card details button.
7. Enter your customer's Credit Card number, Expiration date, Name on Card, Street address, and ZIP code.
8. Click Save.

If you want to enter their account number on the transaction, you can add a custom field. Let me guide you with these steps:

1. Select Custom form styles on the Gear icon.
2. Locate the transaction template and then click Edit.
3. Go to the Content tab.
4. Click the header section.
5. In the left pane, click + Custom field.
6. Tick the box, and you can enter Account number as its name.
7. Click Done.

If you mean something else, please let me know. I'm here to help you out!

I've also added this article for more information when adding custom field: 

• Import Custom Form Styles For Invoices or Estimates
• Customise Invoices, Estimates, and Sales Receipts in QuickBooks Online

Feel free to get back to me if you need help. Keep safe!