[Issue resolved by the OLX support , at the time of discovery of bug , olx.in was not in scope]
Whenever a user wants to login through the mobile app , the user enters his mobile number and then he is presented with a screen to enter the OTP . The problem is that there is no rate limiting on the number of attempts , since the OTP is only 4 digits long , all the combinations can be tried in a very short span of time hence anyone can login in anyone's account by typing victim's mobile number and trying all OTPs.
Here is the original video and PDF i sent to the OLX Support. https://youtu.be/ds8dOFt_8s4