Problem using Flow to update a Creator record when a task is closed in ZohoCRM

I have put together an app in Zoho creator which manages customer cancellations.

One of the creator workflows involves creating a task for a colleague when a new cancellation form record is submitted. This works fine and the task fields include a field called "CancellationID" which is the ID of the creator record.

I have set up another workflow in creator using deluge code so that when a field in the Creator record called "Status" is updated in Creator ( subject to certain conditions) - the task is closed in the crm. This works fine.

I now need a workflow to do the opposite - if the task is updated ( to closed) in the CRM - I want the creator record to also be amended - ie "Status" field updated.

I have set up a Flow to do just this but the mandatory "Record ID" field needs to pull the CancellationID field from the task. This field is not available in Flow - despite it being present in the standard tasks template!

If I put in an actual creator record ID the flow works fine.... Has anyone got any ideas why the CancellationID task field is not showing up in Flow ????

Thanks

Susan