Thanks for getting in touch. Taking a look at the Curl example from our docs here It looks like the example is missing the content header “Content-Type: application/json” - mine works ok when I add that to the given example.
So if I try something like this :
curl -d '{"order":{"id":1234567891011,"note":"Customer contacted us about a custom engraving on this iPod"}}' \
-H "Content-Type: application/json" \
-X PUT "https://coolteststore.myshopify.com/admin/api/2021-07/orders/1234567891011.json" \
-H "X-Shopify-Access-Token: putyouraccesstokenhere"
I’m able to PUT my note ok to my order via my Curl client. We’ll look into the docs. Hope that helps!