Use "Login with URL/user name".
Username: your email address
PW: your app-password (create a password in Profile → Password / Security → App passwords → Mobile App (+ Contacts + Calendar))
Address-book synchronization is one-way (Bitrix24 → Android) and will only synchronize employees (not customers).
To minimize problems please set the address book to "force read-only" inside your DAVx⁵ account.