Column used in the publication WHERE expression is not part of the replica identity

I'm trying to create a logical replication setup where I have a single large database with smaller read replicas branching of filtered on a sub id. For example, if I wanted a subset of items pushed to read replicas for a specific customer, I might have a table on the replication node defined by:

CREATE TABLE public.item (
       id text PRIMARY KEY, 
       data text, 
       customer_id integer
       );

I may or may not have sub_id on the subscription node (not a deal breaker detail). On the replication node, I can add data to the table as I please **until** I create the PUBLICATION like so:

CREATE PUBLICATION customer_items FOR TABLE public.item (
       id, 
       data
       ) WHERE (customer_id = 3);

At this point, I try something like

UPDATE public.item SET
	customer_id = 3 WHERE 
    id = 'GLAMDRING';

I get the error I get an SQL state: 42P10 error, or..:

ERROR:  cannot update table "item"
DETAIL:  Column used in the publication WHERE expression is not part of the replica identity.
STATEMENT: UPDATE public.item SET
	customer_id = $1::integer WHERE 
    id = 'GLAMDRING';

The issue here looks similar . I've recreating the table to remove any ALTER TABLE statements on id, as suggested there, but I have the same result. Most examples I can find that use this logical replication function never make use of the WHERE clause. I'm thinking I've either misunderstood the meaning behind this feature, or I've found a bug/limitation. **Please note:** I am aware that my example seems trivial and should be solved some other way. This is a simplified version of my problem for the sake of brevity. ----- **Update** Trying to use Unique index, as suggested almost got me there.

CREATE UNIQUE INDEX id_customerid_idx ON public.item ((customer_id || id));

But when I try creating a useful PUBLICATION..

CREATE PUBLICATION customer_items FOR TABLE public.item (id, data) WHERE (customer_id || id LIKE '3%');

New error:

ERROR:  User-defined or built-in mutable functions are not allowed.invalid publication WHERE expression 

ERROR:  invalid publication WHERE expression
SQL state: 0A000
Detail: User-defined or built-in mutable functions are not allowed.
Character: 377

Maybe my use-case is a little wild or I need to rethink my application logic to work with these constraints. Am I missing an obvious work around here?