[APP] Aqara & Xiaomi Smart Home - Simplify your life with a smarter home

This is something what Athom has to fix, not the App Developer of the Homey Apps.
So please contact Athom Support → Support | Homey

Btw, negative values can be entered in the WebApp.

Edit

This is what @TedTolboom, the App Developer of the Aqara App, wrote ten days ago about the “external sensor” in a other topic:

So it’s on his To-Do list.