Alertmanager send empty message to Slack

[Huy Phan Ngọc]

Hi guys,

I've setup the Prometheus - Alertmanager model and send alert to Slack, but after some good alert notifications, it always send empty message like the screenshot

My alert manager config:

My alert rule:

Could you please help me what the problem is happening, and what I need to fix to resolve this problem ?

Thank you