Updatable materialized view is a materialized view created with a "for update" clause, with an internal trigger that executes when a DML is performed on the materialized view.
It must be a part of a materialized refresh view group that has the same name as the replication group at the master site.
It must reside on a different database than the master replication group.
You can go through below Oracle documents or reference which explains in detail.
Oracle® Database Advanced Replication
11g Release 1 (11.1)
Part Number B28326-03
Refresh of an Updatable Materialized View - an Overview (Doc ID 759196.1)
How to Create Writeable Materialized Views/Snapshots (Doc ID 189350.1)