Do you have multiple clear photos, accurate description, and is your listing price reasonable? (You can check sold listings on eBay for what similar items have sold for, for comparison.)
If so, it may just take some time for the item to sell.
Do you have a seller history or is this your one and only auction? Do you have positive feedback?
Is the price of shipping too high?
Do you accept returns?
Are you in Japan? When I look at "authentic Mikimoto" on eBay, many of the items are in Japan. I don't know if there are tariffs, but the shipping is very high.