Thanks for getting back to the QuickBooks Community, @AB111.

Allow me to step in and help provide some additional information about the invoice reminder in QuickBooks Online (QBO) UK.

As what my colleague mentioned, regardless if you sent a reminder or an original invoice, QBO will only display the invoice Activity as You: Sent this Invoice. If you'd like to specify that email sent was a reminder, the option is you can write a note to your customer on the Activities tab.

 However, if you're referring to send a reminder and want to reflect automatically on the invoice history, currently QBO doesn't have an option to do this.

It's our priority to provide products and services that suit your business needs. We'll make sure to take note of this and will inform you through this thread once we receive product enhancement update about the availability of this feature.

In the meantime, I'd suggest visiting our QuickBooks Online Blog regularly. This way you'll be updated with the latest news and updates including product improvements. 

Please know that you're always welcome to post if you have any other questions about sending invoice reminder in QuickBooks. I'll be around to help.