Custom smart action on case objects not working

Summary: REST-Based smart actions are not triggering on the Case object

Content (please ensure you mask any confidential information):

We’ve successfully created and tested a REST-based smart action (following the documentation) on the ISR (Internal Service Request) object. For example, we can trigger the smart action to do a simple update to the ISR Title, and this works as expected.

However, when creating the same smart action on the Case object, it does not work:

• Nothing is triggered in the browser network logs.
• No errors are shown in the console.
• The confirmation message does not appear after selecting the smart action (this is the same for both Case and ISR objects).