Fulfillment message is not being saved and other ways to change order timeline

[mpontus]

I'm building an order management app and I want to provide information about the state of the fulfillment in the Shopify admin.

I found that I can make Fulfillment resource with a message property if I use Fulfillment Service API, but I have tried and could not make it work.

I created a Fulfillment Service using REST API and changed location priority to route orders to the new location. I placed a new order and, because the store is not set to fulfill orders automatically, requested fulfillment from my app's location.

I could set the message property when I created the fulfillment request and when I accepted it. This message was reflected in the Shopify admin under the order timeline.

However, this behavior did not extend to when I tried fulfilling the order as my message did not make it onto the page or could be found anywhere in the API response.

I tested this scenario using a fulfillment service and order management app, using REST and GraphQL API. In any case, setting the message property when creating a fulfillment does not have any effect.

I also tried using FulfilllmentEvent as a way to include custom information in the order timeline, but they don't appear to be visible anywhere in the Shopify admin.

I would like to know if there's any way to make Fulfillment's message attribute and if there is any other way to leave custom messages on the order timeline besides FulfillmentRequest resource endpoints.

Thank you.