GoCamera currently does not support the use of the iPhone flashlight for night shots.
The reason for this limitation is that many PlayMemories cameras "are made to work without flash". This means that the cameras set an automatically calculated value for the exposure. When adding the iPhone flash, this usually leads to the results that persons or near objects are overexposed.
Another problem with flash is that it is very hard to time since the response time of the different cameras themselves and the shutter speed differs depending on lighting situation.