It seems

[twicejr]

Take care. Even if a payment fails isSuccessful() returns true!

    //First request
    $gateway = \Omnipay\Omnipay::create('Ideal');


  //// ..........payment occurs after redirect etc.................





 //Request 2:
    if($gateway->supportsCompletePurchase())
    {
          $purchaseResponse = $this->gateway()->completePurchase($parameters)->send();
    }

    if($purchaseResponse->isSuccessful())
    {
          //WILL ALWAYS RETURN TRUE AT THE MOMENT 
    } 

[markdegrootnl]

Please explain

[twicejr]

The payment doesn't have to be succesful, for $purchaseResponse->isSuccessful() to return true.
Even if the payment is not finished, it returns true.

I fixed it by adding the following to src/Omnipay/Ideal/Message/CompletePurchaseResponse.php:

public function isErrorResponse()
{
     return $this->getData()->Transaction->status != 'Success';
}

(see how isSuccessful works in src/Omnipay/Ideal/Message/AbstractResponse.php):::

    return !$this->isErrorResponse() && isset($this->getData()->Acquirer) && $this->rootElementExists();

Do you also think this is the appropriate solution?