I have to test following application as seen below in the price. I am confused about writing test scenario and test cases. Is there anyone who can help me how to write test scenario and test cases by giving few examples?
Considering "classic" architecture where you have back-end, mobile operator which delivers SMSs with OTP and front-end (where user enters received OTP), you have several options to test this functionality.
In order to simplify the testing procedure and make it more applicable for automated testing, I would exclude mobile operator part (as the one related to 3rd party supplier) from the testing by introducing the opportunity to somehow get generated OTP by tester directly (I would consult here with developers in order to see whether this potentially possible in your system).
In this case you'll be able to verify whether the OTP generated by back-end and entered on front-end will be accepted by back-end, without introducing mobile operator into scenario (assuming that this part is stable and corresponds to availability expectations) The simplified scenario looks in this way:
Of course you have also consider corner-cases like: