DB2 for IBM i Series stored procedure call (Laravel)

stored_procedure.php

<?php

use Illuminate\Support\Facades\DB;
use PDO;

class ClassName {

  public static function methodName(String $customer, String $item_number){

    $input_param = 'blah';
    $input_param_2 = 'blah';
    $output_param = '';    // or zero if expecting number
    $output_param_2 = '';  // or zero if expecting number

    $sql = "CALL SCHEMA.PROCEDURE_NAME(:input_param, :input_param_2, :output_param, :output_param_2)";

    $stmt = DB::getPdo()->prepare($sql);

    $stmt->bindParam(':input_param', $input_param, PDO::PARAM_STR);
    $stmt->bindParam(':input_param_2', $input_param_2, PDO::PARAM_STR);
    $stmt->bindParam(':output_param', $output_param, PDO::PARAM_STR, 9);        // Must define length on output param
    $stmt->bindParam(':output_param_2', $output_param_2, PDO::PARAM_STR, 10);   // Must define length on output param
    $stmt->execute();
  }
  
}