Problem with CREATE TRIGGER

Hi
In Postgres 9.1 I have a function as a test (of my ability):

CREATE OR REPLACE FUNCTION insert_payment(integer, numeric)
RETURNS numeric AS
$BODY$
UPDATE company
SET co_payments=co_payments+$2
WHERE co_id=$1
RETURNING co_payments;
$BODY$
LANGUAGE sql VOLATILE
COST 100;
ALTER FUNCTION insert_payment(integer, numeric)
OWNER TO postgres;

This function exists, according to pgAdminIII

So I attempt to create a trigger:

CREATE TRIGGER increment_payments
AFTER INSERT ON payment
FOR EACH ROW
EXECUTE PROCEDURE insert_payment();

ERROR: function insert_payment() does not exist

What am I doing wrong here?

Michael Rowan
mike(dot)rowan(at)internode(dot)on(dot)net

11 Kingscote Street
ALBERTON
South Australia 5014

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