To start using Paytm to make payments for your purchases on the Mi Store app, please ensure that you are using the current version of the app which is 2.6.1 .
To check if you are using the current version, simply head to the Mi Store app, click on ‘account’ which can be seen in the bottom navigation bar, scroll down to ‘settings’ and the app version will be displayed in front of ‘About Mi Store’.