By default, RechargeSMS sends customers notifications whenever their charge fails, including notification if the charge fails due to an out of stock item. You can disable the charge failed notification to prevent customers from receiving all charge failed notifications, including notifications related to out of stock items. 

To disable the charge notification in RechargeSMS:

1. On the Shopify Admin, click Apps and select RechargeSMS.
2. Choose Settings and select Features.
3. Locate the Concierge Features section and toggle the option to “Send Charge Failed Notifications" Off.