Why would the system copy some old sales invoices across but not others. It appears that it has copied those raised in gbp but not euro

Hi, carla-barnes.

Let me help you sort things out. If you're trying to import your sales invoice into QuickBooks Online, you may need to ensure that the multi-currency feature is turn on. Please be reminded that once you this turn on this feature, home currency is set and cannot be changed.

Here's how:

1. Select Settings ⚙️.
2. Select Account and Settings.
3. Select Advanced.
4. Select Edit ✎ in the Currency section and choose your Home Currency.
5. Select the Multicurrency checkbox and confirm that you understand that you can't undo this option.
6. Select Save and close.

It’s definitely worth taking a look at these write-ups to know more about multi-currency feature in QuickBooks Online:

About Multicurrency

How Multicurrency works

If you're referring to something else, please let me know. I'll be around to help you out. Have a good one.