serial.readBytesUntil(10, bufferType, 1); //10 is ASCII code for line feed used for terminating character
Why are you using this? You are not sending a 10, so reading until one arrives is pointless.
Why are you lying to the function? There is plenty of room in the array for more than one character.
If you want to send an int, why not use Serial.parseInt() to read it?