You can view the activity of the invoice you sent to your customer on the Invoices page, Simon.
Once the invoice is sent to your customer and they view it, the invoice activity will be updated to indicate that Viewed is checked.
Here's how you can track it:
- Click the Sales & Get Paid button.
- Navigate to Invoices.
- Click the dropdown button beside the Receive payment link of the sent invoices.

- Select View activity.

From the Invoice Activity, you'll be able to monitor the status of the invoices you've created.
Let us know if you have any further questions or require additional assistance.