I have found several questions about this in 2020 and 2019 and earlier. Unfortunately the answers weren't promising then, maybe it will be better now.
Is there a possibility to charge extra costs for an alternative payment method?
At the moment we use 'Klarna' which is similar to 'Afterpay'. Those payment method let's customers pay after 14 days instead of at the moment of buying. It is used a lot in the Netherlans. At this moment it costs us a lot extra due to the fee Klarna charges to us and us not being able to charge the consumers for this. Especially when consumers buy a product in different sizes in multiple orders which are eligable for 'free shipping', when the sizes that do not fit are returned we lose money on these consumers. These kind of orders cost us money.
I hope there is a solution. Hope to receive a promising answer soon! Thanks!
At this time, it is not possible to charge additional fees should a customer choose an alternative payment method. If you're seeing a lot of orders processed through Klarna and/or you're seeing an increase in return orders, then you could consider working these costs into the product pricing. An increase in the product pricing will help you recuperate the costs you're losing, while still being able to offer Klarna and free shipping. Alternatively, you could also impose a return shipping fee, while still offering free shipping. That may deter customers from purchasing multiple sizes. An accurate sizing guide for your clothing would also help with reducing the number of returns you see.