Error 503 the speciefic adress is not a valid bluetooth MAC adress

MIT App Inventor Help
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Arduino should send:

Serial.print(distance1);
Serial.print("|");
Serial.println(distance2);
delay(300);

println means text with end of line, end of line is \n, it is code 10.
Check ASCII codes.

App Inventor. Designer. BluetoothClient. DelimiterByte: 10
it means that when it receives end of line, character 10, it shows the message.

Here many examples