If you signed up with Google or Facebook account, you must sign in with Google or Facebook account, not the general sign-in way we provide.
Even if you signed up with Google or Facebook account, if you set a password, you can sign in via the general sign-in way we provide.
How to set a password:
1. Go to Account page of settings after sign in your account.
2. Click 'Edit' button(pencil image) next to the Password
3. Set a password and click 'Save'.