Adding @Moore, Kyle comment/solution as answer to this QnA post:
"I am using Invoke-RestMethod in PowerShell. The fields in the output display in the above way if I echo a message object, but if I instead echo only $message.sender for example, it displays the full content of the array as expected. So, the API is returning the information I need, but PowerShell was for some reason failing to display it properly. But if I attempt to manipulate the child objects directly, I am able to do what I need. If I convert the output to JSON, it also seems to fix the display issue when echoing/printing."