Hey there, kbs24.
Thanks for connecting with us here in the Community! I'd be happy to provide some information.
Although QuickBooks Online provides the option to export your customers when you need to, there isn't the option to add their ID. This guide will provide steps on how you can export your customers without running into any issues.
I recommend taking a look at third party apps, you may be able to find something that can help you. I can see how being able to export customer ID's would be beneficial for you, so I encourage you to leave feedback for our developers. Comment are viewed and considered as they create new features and updates for QuickBooks.
If you have any other questions, feel free to reach back out here.
