"invalid reference to FROM-clause entry for table" in Postgres query

Explanation for the error

The immediate cause for the error message is that any explicit JOIN binds stronger than a comma (,) which is otherwise equivalent to a CROSS JOIN, but (per documentation):

Note: This latter equivalence does not hold exactly when more than twotables appear, because JOIN binds more tightly than comma. For exampleFROM T1 CROSS JOIN T2 INNER JOIN T3 ON condition is not the same asFROM T1, T2 INNER JOIN T3 ON condition because the condition canreference T1 in the first case but not the second.

Bold emphasis mine.
This is the cause of your error. You could fix it:

FROM  appointment_intakesCROSS JOIN LATERAL jsonb_object_keys(data #> '{products}') keysINNER JOIN appointment_intake_users ON ...

But that was not the only problem. Keep reading.

One might argue that Postgres should see that LATERAL only makes sense in connection with the table to the left. But that's not so.

Assumption

I added table aliases, and table-qualified all column names as suspected. While being at it, I simplified the JSON references and trimmed some noise.This query is still incorrect:

SELECT i.data ->> 'id'          AS id,       i.data ->> 'name'        AS name,       i.data ->> 'curator'     AS curator,       i.data ->  '$isValid'    AS "$isValid",       i.data ->  'customer'    AS customer,       i.data ->  '$createdTS'  AS "$createdTS",       i.data ->  '$updatedTS'  AS "$updatedTS",       i.data ->  '$isComplete' AS "$isComplete",       count(k.keys)::numeric   AS "numProducts",       u.created_atFROM   appointment_intakes i     , jsonb_object_keys(i.data -> 'products') AS k(keys)JOIN   appointment_intake_users u ON u.appointment_intake_id = i.id#{where_clause}GROUP  BY i.id

Raw query

Based on the above and some more assumptions, the solution could be to do the count in a subquery:

SELECT i.data ->> 'id'          AS id,       i.data ->> 'name'        AS name,       i.data ->> 'curator'     AS curator,       i.data ->  '$isValid'    AS "$isValid",       i.data ->  'customer'    AS customer,       i.data ->  '$createdTS'  AS "$createdTS",       i.data ->  '$updatedTS'  AS "$updatedTS",       i.data ->  '$isComplete' AS "$isComplete",       (SELECT count(*)::numeric        FROM   jsonb_object_keys(i.data -> 'products')) AS "numProducts",       min(u.created_at)        AS created_atFROM   appointment_intakes iJOIN   appointment_intake_users u ON u.appointment_intake_id = i.id--     #{where_clause}GROUP  BY i.id;

Since you only need the count, I converted your LATERAL join into a correlated subquery, thereby avoiding the various problems arising from multiple 1:n joins combined. More:

• What is the difference between LATERAL JOIN and a subquery in PostgreSQL?
• Two SQL LEFT JOINS produce incorrect result

You need to escape identifiers properly, use a prepared statement and pass values as values. Don't concatenate values into the query string. That's an invitation for random errors or SQL injection attacks. Recent example for PHP:

• Problems with my attempt to implement an UPSERT