Query the current value size of the specified BLECharacteristic.
bleCharacteristic.valueLength()
None
// Bluetooth® Low Energy LED Switch Characteristic - custom 128-bit UUID, read and writable by central
BLEByteCharacteristic switchCharacteristic("19B10001-E8F2-537E-4F6C-D104768A1214", BLERead | BLEWrite);
Serial.print(“value length = “);
Serial.println(switchCharacteristic.valueLength());