I tried that format in your screenshot already, and it gives the same error.
So for both:
....."qualityCode": "1", "value": data.JUICER_POW.toString() },
&
......"qualityCode": "1", "value": (data.JUICER_POW).toString() },
It gives the same following error:
TypeError: Cannot read property 'toString' of undefined
I also tried this format:
.... "qualityCode": "1", "value": String(data.JUICER_POW) },
But then I get this error message:
Error: Data doesn't match the configuration! Errors: [{"keyword":"str_integer","dataPath":".value","schemaPath":"#/items/select","params":{"keyword":"str_integer"},"message":"should pass \"str_integer\" keyword validation"},{"keyword":"str_integer","dataPath":".value","schemaPath":"#/items/select","params":{"keyword":"str_integer"},"message":"should pass \"str_integer\" keyword validation"},{"keyword":"str_integer","dataPath":".value","schemaPath":"#/items/select","params":{"keyword":"str_integer"},"message":"should pass \"str_integer\" keyword validation"},{"keyword":"str_integer","dataPath":".value","schemaPath":"#/items/select","params":{"keyword":"str_integer"},"message":"should pass \"str_integer\" keyword validation"},{"keyword":"str_integer","dataPath":".value","schemaPath":"#/items/select","params":{"keyword":"str_integer"},"message":"should pass \"str_integer\" keyword validation"},{"keyword":"str_integer","dataPath":".value","schemaPath":"#/items/select","params":{"keyword":"str_integer"},"message":"should pass \"str_integer\" keyword validation"}]