Laybuy's commission fee is inclusive of GST.
The correct way to treat our commission is that we purchase the products from the merchant at a discount equal to our commission rate. In loose terms, on a $100 basket, we purchase that basket for $95 (assuming a round 5% commission).
We account for GST when we sell the item through to the consumer for the full $100 ($13.04 - our liability).
The merchant only has a GST liability on the sale of $95 ($12.39).
The merchant’s settlement report shows the figure they can use as a Laybuy buyer created tax invoice - this aligns with their payment overnight.