Is there a way to add a comment to an order's timeline via the REST API ?
If so, what's the scope access ? And how to do this.
Thanks
You cannot add a comment to the timeline. You can see your App's interactions with an order on the timeline, exposed by Shopify, but you cannot inject stuff yourself. If you want to decorate an order with comments, you would add your comment to the order notes. That works fine, but as you can tell, it is not timestamped by Shopify, so it lacks an "official" standing... nonetheless. Just use Notes.
Add comment to an order's timeline in Shopify