CREATE OR REPLACE FUNCTION "public"."test"(int4, json)
  RETURNS SETOF "pg_catalog"."record" AS $BODY$ 
DECLARE
rb boolean;
vld text;
msg text;
clmn_name text;
v text;
codes text[];
msg_param text;
BEGIN
	codes := ARRAY 
		[
		'code1'
		];
	for v in select unnest(codes)

	loop
		IF TRUE --((SELECT NULLIF(json_extract_path_text($2, 'first_param'), '') IS NOT NULL)  AND 
			--(SELECT NULLIF(json_extract_path_text($2, 'sec_param'), '') IS NOT NULL))
			THEN
			IF true -- (json_extract_path_text($2, 'first_param')='2' and json_extract_path_text($2, 'sec_param')<>'9') 
			THEN
				rb := true; vld :='code1'; 
				msg := 'hi there!';
				clmn_name := '1';
				RETURN NEXT rb, vld, msg, clmn_name;	
			END IF; 
		ELSE	

		end if;

	end loop;
END;
$BODY$
  LANGUAGE 'plpgsql' VOLATILE COST 100
 ROWS 1000
;
-- вызываю специально неверно
select * from "public"."test"(1,null) as t(f text);
/*
ERROR:  query "SELECT rb, vld, msg, clmn_name" returned 4 columns
CONTEXT:  PL/pgSQL function test(integer,json) line 26 at RETURN NEXT
*/
-- правим вашу конструкцию RETURN:
CREATE OR REPLACE FUNCTION "public"."test"(int4, json)
  RETURNS SETOF "pg_catalog"."record" AS $BODY$ 
DECLARE
rb boolean;
vld text;
msg text;
clmn_name text;
v text;
codes text[];
msg_param text;
BEGIN
	codes := ARRAY 
		[
		'code1'
		];
	for v in select unnest(codes)

	loop
		IF TRUE --((SELECT NULLIF(json_extract_path_text($2, 'first_param'), '') IS NOT NULL)  AND 
			--(SELECT NULLIF(json_extract_path_text($2, 'sec_param'), '') IS NOT NULL))
			THEN
			IF true -- (json_extract_path_text($2, 'first_param')='2' and json_extract_path_text($2, 'sec_param')<>'9') 
			THEN
				rb := true; vld :='code1'; 
				msg := 'hi there!';
				clmn_name := '1';
				RETURN NEXT (rb, vld, msg, clmn_name);
			END IF; 
		ELSE	

		end if;

	end loop;
END;
$BODY$
  LANGUAGE 'plpgsql' VOLATILE COST 100
 ROWS 1000
;
-- несколько тестовых вызовов (вариации ошибок вызова):
select * from "public"."test"(1,null) as t(f text);
/*
ERROR:  returned record type does not match expected record type
DETAIL:  Returned type boolean does not match expected type text in column 1.
CONTEXT:  PL/pgSQL function test(integer,json) line 26 at RETURN NEX
*/

select * from "public"."test"(1,null) as t(f boolean);
/*
ERROR:  returned record type does not match expected record type
DETAIL:  Number of returned columns (4) does not match expected column count (1).
CONTEXT:  PL/pgSQL function test(integer,json) line 26 at RETURN NEXT
*/


select * from "public"."test"(1,null) as t
(rb boolean,
vld text,
msg text,
clmn_name text
);
--t,'code1','hi there!','1'