There are problems with two of the fields in the action:
"Card Image URL" cannot be blank - make sure an image of some sort is in here. Needs to be a .PNG file and cannot be too big; not sure of the actual size limit. This can't be blank because otherwise Teams will not accept the webhook call.
"Card Theme Hex Color" should not include the pound/hash (#) sign. Just put "DC143C" in this field.
Try that - that should work!
The other thing I'll suggest is to send body text with the alert. For example, using the query shown in your screenshot, pass a field called 'messagetext' to the alert. This is easily done with the strcat command like this:
source="test.log]" "error received" earliest=-5m latest=now | stats count | strcat "Error " fieldfromyoursearch " received " count " times." messagetext
To read more about the strcat command you can read Splunk's documentation here: https://docs.splunk.com/Documentation/Splunk/8.0.3/SearchReference/Strcat
You can also read our documentation on this alert action here:
Hope this helps - please let us know if you still have trouble getting it to work!
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