Can't Send Slack Alert with Image

I’m using grafana alert in grafana cloud. But I can’t send alert with image to slack.
What should I do to send alert like this:
螢幕快照 2022-08-31 10-35-58

I’m using the grafana ver9.1.0 in grafana cloud.
And I’ve already install the Grafana Image Renderer plugin, and set some render config in dashboard json model like this:

Please give me any advice or if it just can’t work on grafana cloud?