Lower payout.

I have done a trial run on a product from my Shopify store that is linked to printful. As a mock customer I payed $36 then as expected printful charged me( as the store owner) the same amount ,Now my issue is the payout I get back is always around $1.50 less so in this case $34.50 is my payout. So I’m not making a profit, it seems I’m paying $1.50 on the customer purchase.