First, we are so sorry for the inconvenience! We try to keep all maintenance on Mondays, our "patch day". You should see an update on our Twitter if we are about to deploy something. This error means we just deployed an update while you were in the middle of a request so your request was interrupted. If you refresh the page, it should be back up within a few minutes.
If you see this error for an extended time, but no updates on our twitter, feel free to hop on our Discord and @Lithxe to get our attention. We will look into it ASAP.