Video :
There are two processes. You can choose either,
Once you call the OTP API we generate OTP and save it in the secured database for defined seconds and then send the SMS to the user. If the user does not receive the SMS, they can ask for a resending.
Once you call the same API with the same mobile number, we automatically generate a voice call and read OTP.
In this process, once you call the OTP API from your server, the user will enter the OTP in the front end and you can save the received OTP from the front end on your server to pass the same for verification. You can use it for the verification process on your server only.
Both processes are secure from our end, but process number 2 is dependent on your security protocols.