Is this a valid JSON now? I made some changes
Here is my flows :
[{"id":"ff0d843c.5e05b8","type":"tab","label":"laman oprek","disabled":false,"info":""},{"id":"81e6b612.bd4468","type":"debug","z":"ff0d843c.5e05b8","name":"","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"payload","targetType":"jsonata","x":740,"y":260,"wires":[]},{"id":"86336189.e237d","type":"serial in","z":"ff0d843c.5e05b8","name":"","serial":"4bff77f8.029b88","x":170,"y":280,"wires":[["25087f18.702cb","31fe5d6.317b0a2"]]},{"id":"25087f18.702cb","type":"ui_text","z":"ff0d843c.5e05b8","group":"119a7de4.6ebb92","order":1,"width":0,"height":0,"name":"","label":"","format":"{{msg.payload}}","layout":"row-spread","x":490,"y":200,"wires":[]},{"id":"31fe5d6.317b0a2","type":"json","z":"ff0d843c.5e05b8","name":"","property":"JSONata","action":"obj","pretty":true,"x":350,"y":280,"wires":[["f514a3f0.6b85d"]]},{"id":"f514a3f0.6b85d","type":"ui_text_input","z":"ff0d843c.5e05b8","name":"","label":"","tooltip":"","group":"119a7de4.6ebb92","order":1,"width":0,"height":0,"passthru":true,"mode":"text","delay":"3000","topic":"","x":460,"y":400,"wires":[["21b8eff3.8f3e7"]]},{"id":"21b8eff3.8f3e7","type":"json","z":"ff0d843c.5e05b8","name":"","property":"payload","action":"obj","pretty":false,"x":600,"y":320,"wires":[["81e6b612.bd4468"]]},{"id":"4bff77f8.029b88","type":"serial-port","z":"","serialport":"COM3","serialbaud":"19200","databits":"8","parity":"none","stopbits":"1","waitfor":"","newline":"1000","bin":"false","out":"interbyte","addchar":"false","responsetimeout":""},{"id":"119a7de4.6ebb92","type":"ui_group","z":"","name":"Received from Arduino","tab":"e2d4c61b.53b908","order":1,"disp":true,"width":"23","collapse":false},{"id":"e2d4c61b.53b908","type":"ui_tab","z":"","name":"Home","icon":"dashboard","disabled":false,"hidden":false}]
and the result :