In order to settle the payment at the convenience store, you do NOT need the physical Smartpit card.
Kindly be assured you can find your Smartpit number via the Sakura Mobile portal website.
If it's your first time to log-in the portal website, kindly refer to this article on How to log in to Sakura Mobile Portal for the first time?
1- After you log in your portal website, kindly click on the three dots on the upper right as shown in the below picture:
2- From the menu, please click on (Account)
3- From the Account page, you can see your personal information, as well as the Smartpit number.
Kindly note you can NOT use 7/11 convenience stores to pay the bill. Thank you for understanding.