ERROR: syntax error at or near "$func$ postgres error

I’m trying to create the function –

CREATE OR REPLACE FUNCTION to_tstz_immutable(t text)
  RETURNS timestamptz
  LANGUAGE sql IMMUTABLE STRICT PARALLEL SAFE
$func$
BEGIN 
    RETURN date_trunc('hour', t);
END
$func$;

When I run this function I get below error –

ERROR: syntax error at or near "$func$

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BEGIN

RETURN date_trunc(‘hour’, t);

END

$func$"
LINE 4: $func$
^

SQL state: 42601
Character: 128

What is the problem with this function?

>Solution :

Your function has several syntax issues:

• You needs as prior to dollar quoting. So perhaps as $$function$$
• You cannot use the data_trunc() function with a text argument for the date parameter. I.e. must be date, timestamp, timestamptz.
• An SQL function does not use/need begin ... end

Adjusting your function for the above becomes:

create or replace function to_tstz_immutable(t timestamptz)
  returns timestamptz
  language sql immutable strict parallel safe
as $func$
   select date_trunc('hour', t);
$func$;