This process will depend on the rules you've setup in your Settings, under Policies > Rules.
Why? POS orders do not have customer addresses associated to them.
So, ultimately, what does that mean? It means that when the portal checks the country of origin of the order, it is null.
This will affect you if you have country-based rules in your policy (in your Settings, under Policies > Rules).
The most common use case is international orders: if you have a rule for international orders using a condition like "Country is not United States", then POS orders will fall into that rule since there is no country associated to those POS orders.
If you have a rule "Country is United States", POS orders will not be caught by that rule either.
What else do I need to check for? POS orders for which you generate return labels will have the same to and from addresses: your warehouse address. This is because we do not have a customer address to fill in the "Ship From" field, so your warehouse address is used instead. This should not impact the shipping for your customer, but it's just something to look out for. If you are not sure if a label can be used, we would recommend getting in touch with your carrier.
But ultimately, you can always use Return Magic to return POS orders, just make sure you understand what your customers will see on the portal so you are able to help them if they have any questions! :)