https://support.servicenow.com/kb?id=kb_article_view&sysparm_article=KB0996215

check html sanitiser:

https://support.servicenow.com/kb?id=kb%5Farticle%5Fview&sysparm%5Farticle=KB0750361

(check the body text of the email in the email logs)

If you are adventurous enough to create your own Actionable Message it is worth validating your action. This can be done at: https://messagecardplayground.azurewebsites.net/The site also has a link to A site where you can design/test Actionable Messages: https://amdesigner.azurewebsites.net/

And of course: https://docs.microsoft.com/en-us/outlook/actionable-messages/

Secondly check logs: The logs for Outlook Actionable Messages are not in the expected script log statements but are found under System Logs ->Application Logs, App Scope: Outlook Actionable Messages

You might see messages similar to:

Invoking adaptive card generator for surveysaborting due to invalid survey instance record: b8d36a58db993010919d5716f4961944Invoking adaptive card generator for approvalsysapproval_approver with valid sysapproval ref is required for actionable contentNot a valid approval record for adding adaptive cards. Adaptive content will not be added.Not a valid approval record for adding adaptive cards. No recipients are available

Adaptive content not returned from generator. Skipping to add adaptive cards