Workflow to trigger when a SalesOrder is fully Fulfilled

Hi, we are trying to create a workfow that will run a suitescript which sends a webhook to a website to update the sales order.

The problem is trying to fire the suitescript with a workflow. When the sales order is shipped, (ie fulfilled)

This is what we have so far:
1. CustomSuiteScript : Type  ‘Workflow Action’,
2. Deployment: script = CustomSuiteScript with Applies to = SalesOrder,
3. Workflow:
type = Transaction,
subtype = SalesOrder,
Execute as admin,
Status = testing,
OnCreate and On View or Update checked,
Trigger = After Record Submit,
EventType = All,
Contexts = All,
Condition = “Old Record : Document Status = Pending Fulfillment”
Ive tried a bunch of conditions however nothing seems to trigger the action.

State Action
Type : Custom Action: Deployed CustomSuiteScript
Trigger On : After record submit
EventTypes : all
Contexts: all
Condition: none
Parameters: none

Testing Procedure
1. Change fulfillment from packed to shipped
this automatically changes the sales order ‘document status’ from Pending Fulfillment to Billed, as seen in the Sales order system information log.

2. Look at the ‘Script Execution log’ – however nothing has fired yet.

Could you let me know if the above is on track, and what condition/s should I be using.

Note: removing the condition fires the workflow correctly when any edit is made to the sales order.

Thanks