Debug RPC Function Creation in Supabase

I'm pretty new to database stuff. I'm using Supabase to create an application where I keep track of the number of likes on certain items ('clicks'). I want to filter items either by the date the likes were added, or by certain categories the items have. So far I have a function that I can call from javascript like: const { data, error } = await supabase.rpc('rpc_test', { "json_params": { "categories": '{"fruits", "test"}', "start_date": "2024-04-16 00:22:35.837547+00", } }) Which should return all items that have a category matching the array I pass in, and the number of clicks that have been created since start_date and before and end_date if provided, or zero if no clicks have been created in that time window. And it so nearly works, but I keep running into errors that I don't know how to fix. The important tables in my database are: Items: | id | name | | -------- | -------------- | | 1 | apple | | 2 | beet | Clicks: | item_id | created_at | | -------- | -------------- | | 1 | 2024-04-09 | | 2 | 2024-04-09 | Categories: | id | name | | -------- | -------------- | | 1 | vegetable | | 2 | fruit | Item Categories: | item_id | category_id | | -------- | -------------- | | 1 | 2 | | 2 | 1 | My function query currently looks like this:

create
or replace function public.rpc_test (json_params json default null) returns table (
  id bigint,
  created_at timestamp with time zone,
  name text,
  clicks bigint,
  categories_arr text[]
) as $$
BEGIN
  RETURN QUERY
    select
      items.id,
      items.created_at,
      items.name,
      click_counts.clicks,
      item_id_to_cat_array.categories_arr
    from
      items
      LEFT JOIN (
          SELECT item_categories.item_id AS itemid, array_agg(categories.name) AS categories_arr
          FROM   item_categories
          JOIN   categories ON categories.id = item_categories.category_id
          GROUP  BY item_categories.item_id
      ) item_id_to_cat_array ON items.id = item_id_to_cat_array.itemid
      LEFT JOIN (
          SELECT item_id as click_item_id, count(c.id) AS clicks
          FROM clicks as c
          WHERE (json_params->>'start_date' IS NULL OR c.created_at >= (json_params->>'start_date')::date)
          AND (json_params->>'end_date' IS NULL OR c.created_at >'end_date')::date)
          GROUP BY c.item_id
      ) click_counts ON click_item_id = items.id
    where
        json_params->>'categories' IS NULL OR 
        (json_params->>'categories')::text[] && item_id_to_cat_array.categories_arr;
END;
$$ language plpgsql;

The only problem with this is that categories_arr never has any data. At various points I've had iterations of this that have worked for gathering the information I want but without the filtering in place. I've tried doing things with GROUP BY and HAVING instead, and I'm not really sure where to go. How can I get more information about what is happening in my query? I would like to see what categories_arr is at every step in the process, but I don't know how to log that information.