What do you do when you get a message that the Integration Manager RPC Server is unavailable? Terry Heley has answers at: community.dynamics.com/gp/b/dynamicsgp/archive/2019/06/25/integration-manager-rpc-server-is-unavailable
Integration Manager RPC Server is unavailable – Microsoft Dynamics GP Community
Development & IntegrationInstall, Upgrade & Admin
Archived post from 2019. Dynamics GP and the links it points to have changed since; check current documentation before relying on version-specific steps.