Filter all sibling child items

[StephenSaid]

Hi all, 

I have a bot running which triggers when the Status of the parent changes to 'Submitted'.
I need to run a process that copies a field to another of all the child items of this parent.

This is what I have now, which is not working.

FILTER(
  "Transfers", 
  IN(
    [TransfersHeaderID], 
    SELECT(
      TransferHeaders[Related Transfers], 
      [_THISROW] = Transfers[_THISROW].[Row ID]
    )
  )
)

Any help appreciated.

Thanks

[StephenSaid · Accepted solution]

To answer my own problem:

REF_ROWS("Transfers", "TransfersHeaderID")

[StephenSaid]

Maybe I spoke to soon. I am convinced that the above is correct, BUT...

When I have more than 1 item related to a parent, I am getting the following error:

It seems to be working fine with one item!

The two keys listed are the correct keys which I need to update. 

I can't figure out what is wrong now!