I currently have 16 storage slots. In the cash shop, if try to buy an 'Add Storage Slots' coupon or click the orange button on the bottom left to add storage slots, nothing happens after I click 'ok' to confirm the purchase. After doing this, I can no longer buy anything in the cash shop at all until I leave and re enter the cash shop. I do not lose any NX when attempting to purchase the slot expansions, and my storage does not increase. I have tried re logging and restarting my computer, neither seem to fix this.
Just for clarification, this is not about player inventory space. The storage I am referring to is the the cross-player storage per account. The storage you access by talking to Mr. Kim, Scrooge in the FM, etc.
Maximum number of Storage slots in Maplestory is 48, just like the Inventory pages. I don't buy much NX in Maple, but those slots are extremely useful and mine are all maxxed at 48. For some reason MapleRoyals storage is bugged.