Me too.

Some of these packs actually have a BMS that uses the same port for charge and discharge. Not sure about this one. There are 3 terminals there, just because that type of connector which is normally used for AC power has 3. The packs I have seen, the middle connector is unused.

If the OP could send a link to the description of where he purchased, there might be some clues there. Otherwise, just guessing.