Let's confirm that this is enabled in your invoice template, @rob179.
 
When you complete and send the invoice, the information displayed on the print page depends on the options you enabled in the gear icon on the invoice page and in the Account and Settings. To ensure everything is set up correctly, please allow the SKU in your invoice template.
 
Here’s how:
 
1. Navigate to the Gear icon and select Custom Form Styles.

2. If you have multiple templates, select the one you need to update and click Edit.

3. Click on Content, then select the second box in the invoice.

4. Check the SKU box and click Done.
 
After completing this step, click the Customise option at the bottom of the page to select the appropriate invoice template.
 
For any additional questions, please reply to this thread.