Does anyone know if its possible to integrate a 3rd party API (like USPS or Postmen) with the Paypal cart? Currently, we calculate shipping by weight and "zone" (technically, we collapse USPS 9 zones into 4). Instead, when it comes to calculating the rate, we would like to have Paypal get the price from an API based on the weight Paypal already knows. Anyone done this or know where to start?
Welcome to the PayPal Community Help Forum. Yes, you are able to manually grant permission to a third party to access specific information in your PayPal account and perform API operations on your behalf.
I've attached a link that provides more detailed information as to how to get started below:
