Here are two methods, it could also be done with a function node
One uses JSONata expression in a change node
The other uses mustache template in a template node
[{"id":"b1c50bd382b75e76","type":"inject","z":"b779de97.b1b46","name":"","props":[{"p":"payload"},{"p":"topic","vt":"str"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","payloadType":"date","x":210,"y":1060,"wires":[["176d336035dfc137","ff4f5412.95355"]]},{"id":"176d336035dfc137","type":"change","z":"b779de97.b1b46","name":"SynoChat","rules":[{"t":"set","p":"headers","pt":"msg","to":"{\"content-type\":\"application/x-www-form-urlencoded\"}","tot":"json"},{"t":"set","p":"payload","pt":"msg","to":"'payload={\"text\":\"' & $$.payload & '\"}'","tot":"jsonata"}],"action":"","property":"","from":"","to":"","reg":false,"x":390,"y":1060,"wires":[["32bb0d03.017b1a"]]},{"id":"ff4f5412.95355","type":"template","z":"b779de97.b1b46","name":"","field":"payload","fieldType":"msg","format":"handlebars","syntax":"mustache","template":"payload={\"text\":\"{{{payload}}}\"}","output":"str","x":440,"y":1120,"wires":[["32bb0d03.017b1a"]]},{"id":"32bb0d03.017b1a","type":"debug","z":"b779de97.b1b46","name":"","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"false","statusVal":"","statusType":"auto","x":660,"y":1080,"wires":[]}]
Hope it helps
