зачем это кривой и нечитабельный код?
String msg="\"{\\\"dt\\\":\\\"2020-07-24\\\",\\\"points\\\"";//преамбула
msg+=":["+String(DS[1])+","+String(DS[2])+","+String(DS[3])+ ","+ String(DS[4])+","+String(DS[5])+","+String(DS[6])+","+String(counts++)...