ORA-06502: PL/SQL: numeric or value error: character to number conversion error ORA-06512: at line 1

<?php
// Connect to Oracle
$conn = oci_connect(" "," "," ");

$compID=$_POST["compID"];
$custNo=$_POST["custNo"];
$answer=$_POST["answer"];

//assemble SQL statement
$query = "begin Enter_Competition_SP('$compID','$custNo','$answer');end;";

//parse statement
$stmt = oci_parse($conn, $query) or die ("Cannot Parse Query");
//run it
oci_execute($stmt) or die ("Cannot execute statement");
oci_free_statement($stmt);
OCIFreeCursor( $cur );
oci_close($conn);
?>

create or replace PROCEDURE Enter_Competition_SP
(var_CompID IN NUMBER, var_CustID IN NUMBER, var_Answer IN VARCHAR2)
AS 
BEGIN 
INSERT INTO 
COMPETITIONENTRIES
VALUES 
(var_CompID,var_CustID,var_Answer); 
END Enter_Competition_SP;

CREATE TABLE  "COMPETITIONENTRIES" 
   (	"CompetitionID" NUMBER(8,0), 
	"CustomerID" NUMBER(8,0), 
	"Answer" VARCHAR2(30), 
	 CONSTRAINT "PK_COMPETITIONENTRIES" PRIMARY KEY ("CompetitionID", "CustomerID") ENABLE
   )
/