TFC agent fails to start or exits with Error: “unsupported protocol scheme” when registering to Terraform Enterprise

Problem

This error is encountered when attempting to start a TFC agent:

[ERROR] agent: Failed starting core plugin: error="failed configuring core: agent registration failed: POST /api/agent/register giving up after 1 attempt(s): Post "/api/agent/register": unsupported protocol scheme

Prerequisites

• You are attempting to connect the TFC agent to a Terraform Enterprise installation

Cause

• The address provided as the value for the TFC_ADDRESS variable, or the -address flag is missing the protocal scheme

Solutions:

• Prepend  https:// before the hostname of your Terraform Enterprise installation for the value of the TFC_ADDRESS variable or -address flag