Can I use your app?

If you have a postnl API Key Yes you can!

why does the shopify+ plan pay more?

We try to keep the pricing as reasonable as possible, adding a higher charge to the shopify+ merchants seems to be fair, since these types of stores generate a lot of requests and load on our servers, to be able to offer a reliable service we need to cover the costs for hosting and maintainance, and try to distribute these costs as fairly as possible.

Can you help me set this up?

Sure, you can always contact me at [email protected]