More likely you have an outdated homeassistant installation. The docs always refer to the latest available release, and the ability to use input numbers there are part of the most recent release as of yesterday.
Another observation here is that the code quoted is exactly a lift from the docs, presumably you actually have these two input numbers defined somewhere?
@anon43302295: really thank you. reinstalled right now the HA image, put back on the yaml and the automation has been created… gone crazy for a couple of days trying the example.
Yeah, I suspect that you were unlucky and downloaded the previous version just after the docs were updated, but just before the new version was available for download.