Maker API allows external HTTP GET (browser URL) access and control to your authorized devices.
For example, you can get the status of a device in a JSON object or send a command to a device (and get a response of the device back in JSON)
The reason it is called "Maker API" is it is specifically targeted to the maker community that needs simple URL based local access to specific devices.
If you are not a Maker or Developer it probably has very little use to you unless you want browser URL based control of a specific device.
The app itself has several examples of how to use it.
Without more information, the only thought is did you put access_token= at the end of your request? This error is typically syntax related. If you want to PM me the url I can take a look at it.
Or you can wait for the next release and we will have cloud and local endpoints in the app for you to use.
Yeah that's where I copied the beginning's of the URL from to start with... kinda hokey-pokey of copying a part of a url from a forum post then adding to that a piece from the Maker API screen then having to go back and double check and clean up.
Could be simpler of having the "Example" URL in the Maker API page like it is for the Device Info and Command Send URL