I'm working with the API for the first time, and though I've successfully manged to retrieve data, I'm struggling to update.
I have an order which I'm trying to update by setting the custom_status to {"id" : 4} which corresponds to "Processing" in our system.
The code I'm sending looks like this:

'status': '{"id":1}',
'custom_status': '{"id":4}',
'order_number': bundle.inputData.order_number,
'do_process': 'true'

with the order_number being populated by the user, and is a valid order number.

The response would seem to indicate that I've been successful:

"updated": 1,
"unchanged": 0,
"payments_failed": 0,
"emails_sent": 0,
"processed": 0,
"payments_taken": 0


However, when I look back at the admin orders dashboard the order is unchanged.

Can anyone advise?

Thanks in advance