Your screenshot shows an invalid expression, because the double quotes are wrong. In general you can't paste JSON unmodified in to an expression, because " starts and ends string expressions, and the " around JSON properties will cause syntax errors. You have a few options to work around that:
- use "" inside a string to produce a single character without ending the string
- paste it in to a Text object or some other plaintext object and use that object's text as an expression
- paste it in to a project file and load it with AJAX