Maybe you are using developer edition of salesforce for development purpose and let me guess, you login from different computers to your dev org, salesforce asked every time two-factor authentication code, i.e, OTP sent to your email, maybe you don’t like this thing always, then you need to grant NETWORK ACCESS by providing IP range so that you don't need to enter OTP, but here is another way so that you don’t need to provide OTP, the option to disable Salesforce’s two-factor authentication.
Let me tell you how to disable two-factor authentication in Salesforce:
1. Go to SETUP, and type ‘session settings’.
2. Scroll down to ‘Session Security Levels’
3. Select Two-factor authentication from High Assurance.
4. Now click on Remove and then Click on save.
That’s it! Now you don't require a one-time password. Enjoy!