From your descriptions, here is what I know:
- You are sending data to a POST handler.
- That POST handler is receiving the data.
- You are stringifying the data.
- You are trying to use that stringified data.
- Something is wrong with the stringified data, so you can't use it.
What would be helpful to see:
The data BEFORE you send it.
The POST itself (which you can get from browser dev tools)
The data AFTER the POST handler receives it, BEFORE you stringify it.
The data AFTER you stringify it.
What you are trying to do with that stringified data that isn't working.
If you provide that info, I can help you. If you don't know how to provide this info, then I'm not sure what else I can do.