How to refresh a task via API using the guid-id?

If you want to refresh a task using the guid-id, you need to find out the integer id, this can be done in the PowerShell:

First you need to pull every task available:
$alltasks = irm 'https://<server>/api/task?archive=false' -UseDefaultCredentials

Then you need to filter for the one you want to refresh:
$task = $alltasks | Where-Object { $_.WorkflowStepId -eq "<GUID-ID>"}

Now you can use $task.Id to get the integer and run it against the API:
https://<server>/API/Task/Task_RefreshTask