How do I log in to 'Send to Kindle' with two factor authentication enabled

I use the Send to Kindle desktop application to send epub ebooks converted to Mobi format to my Kindle. Since enabling two factor authentication (using Authy code generator), I am unable to log the app in to Amazon and so unable to upload this way.

After submitting the correct email and password, the login box simply refreshes (without any error message):

After finding an Amazon help page (Alternate Sign In for Two-Step Verification) which gives advice on signing in to Amazon apps that don't support 2FA:

1. Enter your sign in information and submit.
2. You will receive an error message saying that your email and password combination are incorrect.
3. You will then receive a security code through text message, or you can generate the code through the authenticator app.
4. Add the security code to the end of your account password on the device or app you are attempting to register and submit again. For example, if your password is “abcdef” and the security code you receive is “12345”, then enter “abcdef12345” in the password field.
   You will then be signed into your Amazon account.

Although point 2. doesn't apply as there is no error message, adding the code from the authenticator app to the end of the password and re-submitting worked and the application logged in successfully.