Disclaimer: I’m part of the development team
Duphlux.com has just been launched and is expected to become a very reliable alternative to OTP codes normally sent to users to verify their phone numbers when trying to make payments using their cards.
It simply works by giving the app(duplux) a missed call. A number is displayed for the user and the user dials the number with the phone number. Duplux automatically ends the call once it goes through, no charges are incurred and your number is automatically verified.
You can agree with me that solves a lot of problems associated with OTP codes such as not receiving the code especially for people that have their devices on do not disturb, or the the code taking too long to deliver and possibly expiring by the time you finally enter the code.
The application is subscribed free for the first month after which a very little amount is charged for further use. Developers here would definitely want to check this out and send your feedbacks(highly appreciated).