QuickBooks integrates with hundreds of third-party software developers. While I’m unable to recommend an app, I can route you to the website where you can look for an application specific to your business needs. From there, you can integrate the app into QBO.

Let me show you how:

Go to this link: Apps help QuickBooks run better.
From there, enter a keyword in the Search field. This action will display a list of apps.
Select one to show the full details of the app, and scroll down to see customer reviews to help you decide which app is best suited for your business type and needs.

Alternatively, you can look for a third-party app outside the QuickBooks website that allows your customer to order and import into your QBO account.

Moreover, please refer to this article to view different details on how importing data works in QBO: Common questions about importing data to QuickBooks Online.

Please don't hesitate to reply to this thread if you have any other questions about handling your customers. I'm just around to help.