Unfortunately, we only refund for server side issues. Accidentally typing 4mil instead of 4bil is a client error, not a serverside issue, as the value that the item is added for is exactly what you typed in.

The user who purchased the item from you may be kind enough to refund you the item or pay you the remaining money to make up the difference for 4bil, but other than that there isn't much that we can do.

Unfortunately, we only refund for server side issues. Accidentally typing 4mil instead of 4bil is a client error, not a serverside issue, as the value that the item is added for is exactly what you typed in. The user who purchased the item from you may be kind enough to refund you the item or pay you the remaining money to make up the difference for 4bil, but other than that there isn't much that we can do.