Last week my coffee maker started giving me the add water error message, even though the reservoir was full. I went through all the troubleshooting steps online, and when none of those worked, they directed me to call customer support. Customer support told me that since my machine was out of warranty, there was nothing that could be done.
Since it's an electronic device, I figured I'd unplug it and see if that did anything. I left it unplugged for about a day and a half, and guess what - it works perfectly fine again. Still dinging Ninja for this because I am sure they know about this and their troubleshooting team could have suggested it. But I hope I can help someone salvage their machine!