PUSHTech™ Multi-Factor Authentication has a unique charging model called «Pay Per Conversion» :

You only pay for successful verifications (i.e. the PIN code you gave us matches the one returned by the end user)
You do not pay for unsuccessful attempts (ie SMS we sent, attempted TTS calls or even completed TTS calls that resulted in no successful verification)

We offer «Pay Per Conversion» to our customers and we are confident in our ability to make it work, but also believe we all benefit when our interests are fully aligned with yours. However please note we also ask you to not abuse this feature by following a few simple guidelines :

Use PUSHTech™ as your primary if not exclusive Verification vendor
Ensure your application clearly explains to users that a verification will take place e.g. require their consent for it to start by placing a button.
Once the user has acknowledged they want to start the verification, display a screen where they can enter the PIN code