Consider a scenario where you have a Phone number-based login system where you send OTP to the phone number using a third-party SMS service and login the user. The third-party service charges 0.02 $ for each SMS and you have allotted 100$ as the balance for the same.
You discover that every hour 100$ is depleted and you have to keep recharging the balance despite not having huge traffic on your website/app.
Is there something wrong going on here?
If yes, How will you fix it?