Something I have found is that the leather of the flap can be very stiff. If the leather was not softened before manufacture, then you get a very stiff, hard sporran. In effect the flap is under 'spring tension' and wants to open as that is its normal 'at rest' position.

You might have to try and soften the leather yourself. If you turn the sporran upside down and let the top curve (which is now the bottom) soak in warmish water for a while till the leather is quite soaked. It should now be more pliable. Dry excess water with a towel. Close the sporran and lie it on a towel in an airy (not necessarily warm) place. A little bit of weight on the top curve might help. Once dry, with any luck, the sporran flap will have taken on the new shape and will want to stay closed.

Regards

Chas