Microsoft's search engine Bing ended support for sitemap pings Aimy Sitemap uses to send notifications (read the official blog post).
To follow the recommendation, we already published a new plugin Aimy IndexNow.
Right now we are working as fast as we can to integrate notifications to indexnow.org in the sitemap workflow as well.
Update
With Aimy Sitemap version 31.0 and Aimy IndexNow 2.0 both extensions work together. Find out more about it!