With the last update (for all editions) there were some changes. Version Password Depot 15.2.0 uses an updated transmission protocol that is no longer downward compatible. Due to the changes, it is currently no longer possible to connect to the server via the mobile editions when using 2FA (two-factor authentication) in the server.
So if you currently want to work with the mobile apps as well, then the 2FA must be deactivated on the server. The connection should then work again via the iOS app.
We are already working on the implementation of 2FA in the mobile editions, so that this is only a temporary problem and in the future it should be possible to log in via 2FA with all clients.