Please add a debug node (set to display the complete msg object) to the output of the node feeding the json node. Then copy and paste the complete output to a reply so we can see what your data looks like. Without seeing the complete msg data there is no way to determine what is happening.
There’s a great page in the docs (Working with messages : Node-RED) that will explain how to use the debug panel to find the right path to any data item.
Pay particular attention to the part about the buttons that appear under your mouse pointer when you over hover a debug message property in the sidebar.
In order to make code readable and usable it is necessary to surround your code with three backticks (also known as a left quote or backquote ```)
```
code goes here
```
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icon.
See this post for more details - How to share code or flow json
