[Help] Private Shop

Hello guys, i got a problem with my private shop. when i try to sell an item in the shop using penya currency and the buyer got a full inventory and buy the item in the shop. the penya will deduct and didn't get the item bcoz the inventory was full. Any idea's how to fix it or hint's guys?:blush:

Edit: the other currency like Perin/Red Chip was fine.