Master-slave replication of two databases at the same time (MySQL)

Question

MySQL

Good afternoon!

There is a Master-Slave scheme for DB1 where the slave is used for redundancy.
Task: add a new DB 2 database to the Master so that this DB2 replicates to the Slave.

Added to the configs of both servers:

replicate-do-db = DB1
replicate-do-db = DB2

Restarted the servers, and on command SHOW SLAVE STATUS; I see that replication for some reason did not fall. I have not uploaded the DB2 database dump on the Slave yet.

Questions:
1) What am I doing wrong?
2) If I set up a replica, how will it collapse in case of problems? (for example, if suddenly someone made an INSERT into which table on the Slave in one of the databases)

Thanks in advance!