When you log into the Vamp app, if you choose to login with Facebook there are two options. If you choose to login using your Facebook account phone number/email and password (rather than the Facebook app), you may need to provide a code as part of Facebook's two-factor authentication.
The code can be found under the "Code Generator" in Settings on your Facebook account.
If you opt to get the code from your Facebook App, when you return to the Vamp app you may find that you go back on the login screen. Just resume log in again using your phone number/email and password and enter the code you just generated. The Facebook code will last for 30 seconds so you'll need to be quick!
Alternatively, open up the code generator on your Facebook account on a separate device (e.g. desktop) so that you are not logged out of the Vamp app.