Thanks for getting back to us, @eileen-mckechnie.

In QuickBooks Online (QBO), you can only add one serial number (SR) using the Description or the SKU field. The option to add a custom field for each line item is currently unavailable.

Since you need to include more than one SR of each item, the only way that I can think of is to create the items separately as a workaround. Then, instead of adding it on the Description or the SKU fields, you may enter next to the name (to avoid duplicate names).

I can see how having this option would be helpful for you, and I'll take note of this. In the meantime, I recommend visiting our Blog site. This is where we share recent happenings and future developments, such as updates to newly added features. Here's the link: https://quickbooks.intuit.com/blog/.

For tips and other resources, I suggest visiting our website for reference: Self-help article.

Feel free to post again or leave a comment below if you have any other questions. I want to make sure everything is taken care of for you. I'll be here to help. Have a good one!