If you are running the On-Premises version of Microsoft Dynamics 365 Business Central, you can install the Commerce 365 for Easypost extension using Windows PowerShell and the app runtime package provided by your implementation partner. You can also download the latest version of the on-prem software by going to our public Github repositories. 

https://github.com/NVision-Commerce-Solutions/Commerce365.Easypost.Public

Publish-NAVApp -Path "X:\apps\Commerce 365 for Easypost_22.0.10000.0.app" -ServerInstance BCX
Sync-NAVApp -Name "Commerce 365 for Easypost" -ServerInstance BCX
Install-NAVApp -Name "Commerce 365 for Easypost" -ServerInstance BCX