Both the email and the password are case sensitive - make sure they're entered with the capitalisation used when signing up.
If you signed up using Facebook, always use your Facebook as login. If you forgot your password, you have to ask Facebook to reset it.
If you signed up using Google, always use Google as login. If you forgot your password, you have to ask Google to reset it.
If you signed up using your email, always use email when you log in. If you forgot your password, we can reset it for you. Just click 'forgot password'.
First 'Sign In'
Tap 'Forgot password for email?'
Enter your email address. If you don't remember which email address you used for sign-up, check your email archive for emails from firstname.lastname@example.org
If we have your email address on file we will send a reset link. The mail is sent from email@example.com - make sure to check the spam folder if you can't find it.
The email will look like this and the link is valid for 24 hours. Tap 'Reset Password'.
You will be directed to a website to set your new password.
And if the two match (and are sufficiently strong), you will get a confirmation that your password has been changed. Reopen the app and sign in with your email and new password.