How to resolve error Syntax error

What happened

When you're viewing an Adaptive Card on your dashboard you get the following error message:

Error: syntax error at line 1:25 Invalid expression format.

Why is this happening?

The Adaptive Card's payload, which is formatted as JSON, cannot be rendered as it contains an invalid expression.

How to fix it

Open the affected Adaptive Card in the Designer. Then, one-by-one remove some elements from the Card, toggling into the Preview mode after each change, to see if the affected portion of your Card's payload has been deleted. This will require knowledge of correct JSON syntax.