https://hacksbyme.net/2019/11/14/deployments-to-dxc-s-using-api-with-octopus-deploy/

DeployFromSourceStep1.ps1

# DXC-S deploy from source environment to target environment. Step one that deploys to a slot on target.

# Install the EpiCloud module
if (-not (Get-Module -Name EpiCloud -ListAvailable)) {
    Install-Module EpiCloud -Scope CurrentUser -Force
    Write-Output "Installed EpiCloud module"
}

Connect-EpiCloud -ClientKey $OctopusParameters["DXC-S API Key"] -ClientSecret $OctopusParameters["DXC-S API Secret"]

# Check if there is an ongoing deployment
$deployments = Get-EpiDeployment -ProjectId $OctopusParameters["DXC-S Project Id"]
$ongoingdeployid = 0
Foreach ($deployment in $deployments) {
    if ($deployment.parameters.targetEnvironment -eq $OctopusParameters["DXC-S Target environment"] ) {
    	if ($deployment.status -eq 'AwaitingVerification' -Or $deployment.status -eq 'InProgress' ) {
          $ongoingdeployid = $deployment.id
          Write-Host $deployment
          break
      	}
    }
}

if ($ongoingdeployid -eq 0) {
	$deployment = Start-EpiDeployment -ProjectId $OctopusParameters["DXC-S Project Id"] -SourceEnvironment $OctopusParameters["DXC-S Source environment"] -TargetEnvironment $OctopusParameters["DXC-S Target environment"] -SourceApp cms -Wait
}
else {
	Write-Warning "There already is an ongoing deployment ($ongoingdeployid), skipping this step." 
}