I edited the invoice to include an order number by adding sku but changing the field name to order number. I see sku in the invoice but cannot add anything int he fiel

It's my pleasure to help you today, userworkingnotary.

SKU in QuickBooks Online (QBO) can be added by going through each item on your Products and Services window. This will automatically show up on your invoice once you use the item.

I'll show you how to do it below:

1. Go to Sales and choose Products and Services.
2. Select the item you want to change the serial number and click Edit.
   
3. From the SKU field, enter the correct serial number.
4. Click Save and close.
   

The items used on your invoices should now have the updated serial numbers. You might want to visit this article to learn more about adding product and service items to QuickBooks Online.

Since SKU is designed to have it's default field on your invoice, you'll want to add a custom field for the order number. 

Here's how to do it:

1. Go to Gear icon and choose Account and Settings.
   
2. Choose the Sales tab.
3. Click the Sales form content.
4. Under Custom fields, enter Order number in one of the Name field and check the boxes for Internal or Public, depending on your preference.
5. Click Save and then, Done.
   

Learn more about adding custom fields through this article: How to add custom fields to invoices.

Here's what it looks like after adding the item with SKU on your invoice together with the newly added order number field.

The Community is always open if you have other questions. I'll be around to help. Wishing you a great day ahead!