Error when alerting to Discord


I am trying to setup a Discord Alert from Grafana. I have created a webhook in Discord and have entered it in grafana:

However when I am sending a test alert, it it not published and Grafana log gives me the following error:

t=2018-12-03T19:11:19+0100 lvl=info msg="Sending alert notification to" logger=alerting.notifier.discord webhook_url=***my_web_hook_(hidden)***
t=2018-12-03T19:11:19+0100 lvl=eror msg="Failed to send notification to Discord" logger=alerting.notifier.discord error="Webhook response status 400 BAD REQUEST"
t=2018-12-03T19:11:19+0100 lvl=eror msg="failed to send notification" logger=alerting.notifier id=0 error="Webhook response status 400 BAD REQUEST"

Is there something wrong in my configuration?
Grafana version: Grafanav 5.3.4 (commit: 69630b9)

Ok I found the issue:

in grafana.ini I had a root_url which was not a fully qualified hostname.
When replacing

root_url = http://myserver/grafana


root_url = http://myserver.mydomain/grafana

the alerting worked!