Difference between password and encryption key

The difference between the password and the encryption key can be confusing.
Password and encryption key are two different things :
- you will use your password to enter, unlock the app (and decrypt synchronized data),
- you will have to enter your encryption key to decrypt a backup.

So, when you try to import your backup, you have to enter your encryption key, which may be different from your password (depending on what you set at the time you exported your backup).