I would really like to see the Maker API provide an error response (possibly just a message through the post URL) if a 3rd party system sends a command to a device through the Maker API and the device is, for whatever reason, unavailable and the command is not carried out. This could be because a Zigbee/Z-Wave device is offline or an IoT device that works through a cloud service can't be reached because the cloud service is down.
To illustrate the need here is an example. I live in a ski town and there are people who have multi-million dollar homes (I wish I was one) that come into town a week or two a year and rent their homes out when they aren't using them. They typically have a property management company take care of their home when they aren't there. They also might have a Hubitat hub to control the lighting, HVAC, etc. in the home since smart homes rent for higher prices. The property management company could have software to remotely manage the home that connects to the Hubitat through the Maker API.
In the fall, when the house isn't occupied we will suddenly get some cold weather. So the property management company remotely connects to the home and turns on the heat. Unfortunately, the cloud service for the IoT thermostat was down so the command didn't go through. With the heat off the temperature in the house drops, a pipe bursts, and there are tens of thousands of dollars of damage to the home. All of this could have been avoided if an error message was sent back to the property management company's software system. Then they would have simply dispatched someone to the home to manually turn on the heat.
This is real world. Every year people forget to leave their heat turned on in a vacation home and when the temperature drops too far in an unattended house a pipe bursts.
The Maker API really should have a mechanism for reporting an error to the connected system. A simple json message to the postURL address would be more than sufficient.