Welcome and thanks for posting in the Community, @oogie.

In QuickBooks Self-Employed (QBSE), creating reports per product based on the invoices and linking the postage from PayPal is currently unavailable. You need to manually enter them, then export the invoices to Excel to produce a report as a workaround.

To generate an invoice, here's how:

1. In QBSE, go to the Invoices menu at the left pane to get to Create invoice. 
2. Enter the necessary information.
3. Once done, click  Send invoice to email your invoice. You can also select the arrow and Preview to review.

For more information, consider checking out this article: Create an invoice in QuickBooks Self-Employed.

After that, here's how to export them to Excel:

1. Go back to the Invoices menu.
2. Click the drop-down arrow under the Action column.
3. Pick Export as PDF.

I'll pass along your suggestion to our Product Developers. They're always looking for ideas to consider on how to improve QBSE. In the meantime, I recommend visiting our Blog site. This is where we share recent happenings and future developments, such as updates to newly added features.

Just in case, I'll add this article for future reference: Connect bank and credit card accounts to QuickBooks Self-Employed.

Please know that I'm only a post away if you have any other issues or concerns. I'll be more than happy to help. Have a good one!