Thank for using our module and thanks for contacting us.
I am using your Agile Paypal module, it works perfectly but we have a few overseas orders are not being charged the correct amount of shipping/postal costs.
I guess your issue is related to the shipping configuration of your PrestaShop. I have another customer had the similar issue a few days ago, but it is fixed by correct shipping configuration. It is difficult for me to figure out the problem.
I can give you admin access of my development site, if you can configure my development site the same way of your PrestaShop store, and make the problem appears on my development enviropnment, I will try to debug it and find out cause of your problem and help you fix your problem.
Please let me know if you would like to proceed.