Why can't I setup replication with pglogical? It says I need a primary key even though I have unique constraints

Question

I'm trying to enable replication with pglogical on a database running Postgres 9.6.22, however I can't add one of my tables even though it has a unique constraint:

db=> SELECT pglogical.replication_set_add_table('default', 'public.tablename');
ERROR:  table tablename cannot be added to replication set default
DETAIL:  table does not have PRIMARY KEY and given replication set is configured to replicate UPDATEs and/or DELETEs
HINT:  Add a PRIMARY KEY to the table

The documentation says I should be able to add it with a not null unique constraint- I have that:

db=> \d+ tablename
                                         Table "public.tablename"
    Column     |           Type           | Collation | Nullable | Default | Storage  | Stats target | Description
---------------+--------------------------+-----------+----------+---------+----------+--------------+-------------
 col1          | character varying        |           | not null |         | extended |              |
 col2          | character varying        |           | not null |         | extended |              |
 col3          | timestamp with time zone |           | not null |         | plain    |              |
 col4          | jsonb                    |           | not null |         | extended |              |
Indexes:
    "idx1" btree (lower(col1::text))
    "unique" UNIQUE CONSTRAINT, btree (col1, col2)
Foreign-key constraints:
    "fkey" FOREIGN KEY (col1) REFERENCES anothertable(col1) ON DELETE CASCADE
Replica Identity: FULL

What am I missing? I can't add a primary key

Answer 1

alter table ... replica identity using index <unique index name> did the trick; replica identity full doesn't work.