This post might seem off topic or sort of too much of common sense, but some people are still having difficulty in crossing this step of facebook login approval when logging into facebook from new browser on their computer.
When logging in on your facebook account for which you have turned on login approvals from your computer, facebook asks you to enter a code on the very next page when you login.
As you can see, it asks you to enter the security code from your code generator which is in your smart phone.
People might get confused that what should they enter, when they haven’t received the text with code from facebook, well this is not the input box for any sms code, so Facebook hasn’t sent the sms yet. If you read “carefully” this is the login box which allows you to enter the code generated from your mobile / smart phone running Facebook already and logged in with same account which you’re trying to login here on your computer. In the settings you can find the code generator.
However, if you want Facebook to send you the approval code sms, you have to click “Can’t find your code?” and it will open a popup which looks like this:
Instead of getting confused with the given details and options, simply click “Text me a security code” and Facebook will send a security code to your mobile phone number which you added earlier while turning on the Login approvals in security settings.
Hope this helps! :)