Cloudflare tunnel -> Webhook ... only supports PUT,POST methods but GET was received from

I’m trying to configure an access for my HA instance over Cloudflare Tunnel.
The tunnel is operative and if I access HA from the internet using the web page it simply works.

When I try with the official app, it seems to close and then opens a browser and tries to access the HA instance at https://mysub.mydomain.com/lovelace?external_auth=1.
Then it shows a connection error, retry countdown, etc… on the browser and the HA logs shows:

Webhook [REDACTED] only supports PUT,POST methods but GET was received from [REDACTED]

I’ve tried so far configuring the http section with the use_x_forwarded_for: true line and the trusted proxies.
I don’t know what else to do.

Change the yaml maybe?
Automation Trigger - Home Assistant.