Click on Send SMS tab in the Menu bar-
1. If the message is shown as sent then go to https://msg91.com and check the message in the Delivery Report.
2. If you are unable to find the message in Sent Messages logs, then, from your Cpanel, open the WHMCS database in PHP-myadmin and search for MSG91.
3. Click on the table name with the setting suffix and check for the latest entry. You will see the APIs in the logs column.