I've come across this error with Firebase saying too many requests. I've read the nest api saying that they have limited the number of requests to avoid battery drainage on the device. But on the official nest android app you can switch on/off (changing to heating/off) the thermostat without an issue.
Any idea why this is limited in the developer api?
The API limits the number of requests to preserve battery life and it will also stop accepting requests completely if the battery level drops too low. Take a read through this page on the Nest API site about limitations.
I would expect if you keep flipping the on/off switch in the Android app, it would also quit working after a while. You can pull up the battery state and look at it, so maybe someone will determine what the upper/lower limit is?