Hi @Sam_L,
Before you get the value 'Description' of task details, you should make sure there is a value in the task description, you can create the task description in the task board:
Then you can use the action Get task details to get the dynamic content of Description.
Hope it can help you.
Best Regards,
Community Support Team _ Lin Tu
If this post helps, then please consider Accept it as the solution to help the other members find it more quickly.