Return value from WITH clause in PL/pgSQL

I am attempting to RETURN an integer from a plpgsql MERGE-related action that uses WITH. The value I want to RETURN is within the WITH statement below - the id. The error I receive with the below code is as follows:

relation "post_insert" does not exist"

Explaining the code: This code might not be the most efficient way to do the below, but I am setting things up to work for some future use cases where I think I will need to use other features of MERGE. All this does is create a post through Post_Insert, and then using that Post_Insert (which returns the post's id), I create rows in the Hashtags_Posts table that relate back to a master hashtags table.

The "RETURN (SELECT id FROM Post_Insert)" is what is causing the problem. I cannot seem to get the id from Post_Insert and return it.

Any help on how to access the id in Post_Insert would be greatly appreciated.

  create or replace function createPost(  uid_query text,   post_text_query text default '',   text_url_query text default '',   photo_url_query text default '',   video_url_query text default '',   audio_url_query text default '',  location_query text default '',  tags_array_query text[] default '{general}',    photo_query boolean default false  )returns integer language plpgsql as $$BEGINWITH Post_Insert AS (  INSERT INTO "Posts" (    author,     post_text,     text_url,     photo_url,     video_url,     audio_url,     location,    photo  )  VALUES (    uid_query,     post_text_query,     text_url_query,     photo_url_query,     video_url_query,     audio_url_query,    location_query,    photo_query  )  RETURNING id)MERGE INTO "Hashtags_Posts" HP USING (SELECT *         FROM "Hashtags" H        WHERE  H.hashtag = ANY(tags_array_query))        as TMTON HP.id = (SELECT id FROM Post_Insert) AND TMT.id = HP.hashtag_idWHEN NOT MATCHED  THEN  INSERT (post_id, hashtag_id)        VALUES ((SELECT id FROM Post_Insert), TMT.id);RETURN (SELECT id FROM Post_Insert);END $$