Sinch Flash Call Verification allows numbers to be verified without any user interaction at all or for web application verification with minimal user interaction. It works by placing a dropped call to the recipient where the incoming call number is the OTP code, equivalent to the OTP code in an SMS. The code can be processed automatically on Android for a seamless user experience
It is recommended that you do not rely solely on flash call verification and that you should try flash call first and if flash call fails you can automatically fall back to SMS or you can allow the end-user to start SMS-fallback.
You can very simply integrate Flash Call Verification into Android and web apps using the lightweight Sinch Verification SDK or using the Sinch REST API with just a few lines of code.