Data syncing in manually created order's custom field

i want to know , how we can sync the data in order’s custom field via API, i have synced it for contact’s custom field by giving parameter custom_fields and pass the field id and corresponding value or content.

but in order i am not able to sync the data in custom fields of order.

Please help!!

I do not see any Order - Custom Fields support in the REST API v1 Documentation.
Unless @TomScott knows something else?

You can still retrieve the Order Custom Fields using the XML-RPC API instead.
You would need to see the Data Service Query function, and query the “Job” table.
To query the Custom Fields you will need to prefix them with the underscore “_”.

Query Function:

Job Table:

To find the API Name of the Custom Fields, you can do that via the “Admin - Settings - Application Settings - Custom Fields” section. Select “Order” from the dropdown and click on the “Go” button. Right at the very bottom of the page you will see the link “View the field database names (for the API)”, click on it and you will see a popup appearing. You will want the “Database Name” field.

Alternatively you could query the XML-RPC DataFormField table to get a list of the Custom Fields for the Order -