I was doing some work with a client recently to implement Microsoft Dynamics 365 Business Central. While testing in a sandbox environment we encountered an issue when trying to email using the Continia Document Output module.
This error is no just with that module, but with any module or functionality which tries to make outward requests; as a security measure the ability to make outward requests is switched off when the sandbox environment is created.
The request was blocked by the runtime to prevent accidental use of production services