I created a custom user meat value and want to add a new key/value to this array. But somehow I can't get it to work correctly, I always get a new array in side the array so that I always have e new dimension. But I want to keep just one dimension and add the new key/value pair.

I know this is nothing complicated but somehow I can't get it to work. I would appreciate any help.

my entry script:

    $invoice_meta = get_user_meta( $_GET['id'], 'invoices');
    $random = substr(number_format(time() * rand(),0,'',''),0,5);
    if(empty($invoice_meta)) {
        $invoice_array = array();
        $invoice_array[date('d.m.Y').'_'.$random] = $pdf_save_path.$pdf_name;
        add_user_meta( $_GET['id'], 'invoices', $invoice_array);
    } else {
        $invoice_array = $invoice_meta;
        $invoice_array[date('d.m.Y').'_'.$random] = $pdf_save_path.$pdf_name;
        update_user_meta( $_GET['id'], 'invoices', $invoice_array );
    }

The first entry var_dump looks like this:

    array(1) {
      [0]=>
      array(1) {
        ["07.05.2013_51584"]=>
        string(69) "user-data/26/rechnung/tierportal-d_07-05-2013_587543369Y48693K_26.pdf"
      }
    }

after second one it looks like this:

    array(1) {
      [0]=>
      array(2) {
        [0]=>
        array(1) {
          ["07.05.2013_51584"]=>
          string(69) "user-data/26/rechnung/tierportal-d_07-05-2013_5875448693K_26.pdf"
        }
        ["07.05.2013_37016"]=>
        string(69) "user-data/26/rechnung/tierportal-d_07-05-2013_58754348693K_26.pdf"
      }
    }

But I want to look it like this

    array(1) {
      [0]=>
      array(2) {
        ["07.05.2013_51584"]=>
        string(69) "user-data/26/rechnung/tierportal-d_07-05-2013_587543369Y48693K_26.pdf",
        ["07.05.2013_51534"]=>
        string(69) "user-data/26/rechnung/tierportal-d_07-05-2013_587543367Y48693K_26.pdf"
      }
    }