After performing all of the Streaming Replication setup steps,
What replication steps?
database system identifier differ between the primary and standby
How did you take the initial backup of the master? Did you rsync the master filesystem (after issuing pg_start_backup()) or use pg_basebackup, or did you literally take a pg_dump of the master and try to turn that backup into a slave? If the latter, you will need to use the rsync/pg_basebackup method.