When the filament passes beyond the gear mechanism you will notice that the pen has stopped extruding and you will also hear a change in the sound of the motor, meaning an increase in the pitch.
At this point it is necessary to insert a new filament in order to continue drawing.
How to do it:
1 - Take (1x) filament rod out to the filament pack.
2 - Insert the filament in the opening in the back of the pen and gently push the filament while holding one of buttons in order for the gear mechanism to catch it.
Note: When using PLA, since the pen has been preloaded with ABS, it is mandatory to use ABS mode until one inch (~3cm) of filament is remaining outside the back of the pen. In this moment all the ABS plastic has been extruded and you can switch to PLA mode.