Help with BT Data to Text

[groundFungus]

@bigj_3d

while(incomingByte > 0)
    {
      Serial.print(char(incomingByte));
      displayMessage += char(incomingByte);
      incomingByte = Bluetooth.read();     
    }

That while loop runs independently from the Bluetooth.available function.

I suggest that you have a look at the serial input basics tutorial.