JSON validator
Property name must be a string literal
Processed in your browser · nothing is uploaded
Checks JSON against the actual grammar and points at the first thing that breaks it, with a line and column. The sample above has a trailing comma, which is the single most common cause.
How to use the json validator
This validates syntax, not shape. JSON being valid tells you it parses; it says nothing about whether the fields your code expects are present or the right type. That is schema validation, a separate job done with JSON Schema. The distinction matters because "the JSON is valid" gets offered as a reason an integration should work when the real problem is a missing field or a number sent as a string. If you control both ends, a schema catches those; a syntax validator never will.
Questions
The three usual causes are a trailing comma after the last item, single quotes instead of double, and unquoted keys. All three are valid JavaScript and none is valid JSON.