The US consulates in Germany have introduced a new system for booking visa appointments. The new system requires that the contact email is confirmed when creating a profile. In addition, three security questions/answers must be created. These security questions must be answered correctly each time you log in.
The new system has significant problems. In theory, profiles created in the old system can be transferred to the new system so that visa fee payments that have already been made but not yet used can be used. However, this has proven difficult in many cases as previous visa fee payments cannot always be found.
In general, it is common for the system to freeze or shut down unexpectedly, making booking an appointment for a visa difficult or time-consuming.