Hi,
It requires developing a plugin for HikaShop. We have a developer documentation available here:
www.hikashop.com/support/documentation/6...r-documentation.html
If you want the integration plugin to get the rates from goshipppo.com in order to propose them during the checkout, you'll want to develop the plugin as a shipping plugin. You can take an example on the USPS, UPS, FedEx, Australia POst v2 plugins included in HikaShop. They are located in the folder plugins/hikashopshipping/ of your website when HikaShop is installed.
Then, to send the data of the order after the checkout to goshippo.com you want to implement the "onAfterOrderUpdate" event. I would recommend looking at the Matomo plugin for an example of this:
www.hikashop.com/marketplace/product/271-matomo.html
A shipping plugin can do both tasks.