How to fix PL/pgSQL error in PostgreSQL

-- INCORRECT: 2 placeholders but only 1 argument
RAISE EXCEPTION 'Error: % in %', error_msg;

-- CORRECT: 2 placeholders and 2 arguments
RAISE EXCEPTION 'Error: % in %', error_msg, context_info;

-- Use %% to output a literal percent sign
RAISE NOTICE 'Progress: 100%%';

CREATE FUNCTION check_age(user_id INT) RETURNS TEXT AS $$
DECLARE
  age INT;
  message TEXT;
BEGIN
  SELECT user_age INTO age FROM users WHERE id = user_id;
  -- Make sure age is INT and user_age column is compatible
  message := 'User age is ' || age::TEXT;
  RETURN message;
END;
$$ LANGUAGE plpgsql;

BEGIN
  PERFORM 1 / 0;  -- Will raise division by zero
EXCEPTION
  WHEN division_by_zero THEN
    RAISE NOTICE 'Cannot divide by zero';
  WHEN SQLSTATE '22012' THEN
    RAISE NOTICE 'Caught by SQLSTATE code';
END;

BEGIN
  -- Some operation that might fail
  INSERT INTO table_name VALUES (NULL);  -- May violate constraint
EXCEPTION
  WHEN OTHERS THEN
    GET STACKED DIAGNOSTICS
      error_code = RETURNED_SQLSTATE,
      error_msg = MESSAGE_TEXT;
    RAISE NOTICE 'Error [%]: %', error_code, error_msg;
END;

CREATE FUNCTION validate_amount(amount DECIMAL) RETURNS BOOLEAN AS $$
BEGIN
  ASSERT amount > 0, 'Amount must be positive';
  ASSERT amount <= 1000000, 'Amount exceeds maximum';
  RETURN TRUE;
END;
$$ LANGUAGE plpgsql;

-- Enable assertions (on by default)
SET plpgsql.check_asserts = on;

-- Install the extension
CREATE EXTENSION IF NOT EXISTS plpgsql_check;

-- Check a function for errors
SELECT * FROM plpgsql_check_function('my_function(INT)'::regprocedure);