Update Property on a Document from a linked document

I have two documents. Invoice and GRV.

The GRV gets created from the object creator and is then linked to the invoice document via a Property Linked GRV.

The GRV goes through a workflow and the GRV workflow steps updates a Property on the GRV called GRV Status. 

What i want to do is to update the GRV Status Property on the Invoice document as the GRV moves through the workflow.

I have successfully used the property calculator to update this Property on the Invoice Document, however, this only happens if i make a change to the Invoice document. It does not happen automatically.  

I need it to update the GRV status on the Invoice Document as and when the workflow changes.

Any help will be greatly appreciated. 

Below is my config

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