What does the automation in FME do… is it run workspace. Does this workspace have any published parameters, particularly if they are required and there is no default value for that published parameter.

Also check that the credentials being used in the call, that that user has access to run workspace, and has all the web/database connections used within the workspace, also shared to it from fme flow

Thanks for your comment j.botterill but I am getting this error at the very first step of setting webbook as you can see I am getting 404 error means can not reach the webhook URL which is https://xxxxxxxx/fmerest/v3/automations/workflows/4c2cbc0e-3df1-4cbe-9154-b866fe5b6a09/2274b9f3-c600-2ead-a2bc-a20dab4d8db0/message

Not sure why you are commenting on workspace stuff!

here is the Automation 

Rather than using “ping” for testing the network connecting (the test is too broad), check specifically that port 443 is open using Powershell:

Test-NetConnection fme_server_hostname -Port 443

The result should include:

TcpTestSucceeded       : True

Remember to do this from a Powershell command line on the server that is running the ArcGIS Portal service.

A more involved test would be to use “curl” (Linux/Mac/Windows) or the Powershell command Invoke-RestMethod (Windows) on the ArcGIS Portal server to try and trigger the FME Flow webhook from the command line.

If this fails, you need to review firewall and/or proxy settings to let the traffic through.

If you are certain that the connection is open but ArcGIS Portal still refuses to create the webhook, you may want to ask Esri support or in a dedicated forum.

Thanks David, Yes I am getting TcpTestSucceeded  : True, when running PS and Test Net connection command on Portal VM