I don’t know why, but I have a 400: Bad request response. 
Somebody had like that?
DSM 7.0-41890
Record in HA log is:
ERROR (MainThread) [homeassistant.components.http.forwarded] A request from a reverse proxy was received from 192.168.1.2, but your HTTP integration is not set-up for reverse proxies
I found an answer! I have to add to config.yaml
http:
use_x_forwarded_for: true
trusted_proxies: 192.168.1.2