diff --git a/src/Handlers/ResponseHandler.php b/src/Handlers/ResponseHandler.php
index 12d8987..083786b 100644
--- a/src/Handlers/ResponseHandler.php
+++ b/src/Handlers/ResponseHandler.php
@@ -130,7 +130,7 @@ public function retrieveH000ReportText(DOMDocument $xml): string
     public function extractInitializationSegment(Response $response, Keyring $keyring): InitializationSegment
     {
         $transactionKeyEncoded = $this->retrieveH00XTransactionKey($response);
-        $transactionKey = $this->base64Service->decode($transactionKeyEncoded);
+        $transactionKey = $transactionKeyEncoded !== null ? $this->base64Service->decode($transactionKeyEncoded) : '';
         $orderDataEncrypted = $this->base64Service->decode($this->retrieveH00XOrderData($response));
 
         $orderDataCompressed = $this->cryptService->decryptOrderDataCompressed(
@@ -154,7 +154,7 @@ public function extractDownloadSegment(Response $response): DownloadSegment
         $transactionId = $this->retrieveH00XTransactionId($response);
         $transactionPhase = $this->retrieveH00XTransactionPhase($response);
         $transactionKeyEncoded = $this->retrieveH00XTransactionKey($response);
-        $transactionKey = $this->base64Service->decode($transactionKeyEncoded);
+        $transactionKey = $transactionKeyEncoded !== null ? $this->base64Service->decode($transactionKeyEncoded) : '';
         $numSegments = $this->retrieveH00XNumSegments($response);
         $segmentNumber = $this->retrieveH00XSegmentNumber($response);
         $orderDataEncrypted = $this->retrieveH00XOrderData($response);
diff --git a/src/Services/Processor/Base64Encoder.php b/src/Services/Processor/Base64Encoder.php
index 24c5b0f..c8f0630 100644
--- a/src/Services/Processor/Base64Encoder.php
+++ b/src/Services/Processor/Base64Encoder.php
@@ -13,10 +13,10 @@
  */
 final class Base64Encoder implements Base64EncoderInterface
 {
-    /** Max encoded length = 10 * 1024 * 1024 (10 MB) */
-    private const MAX_ENCODED_LENGTH = 10485760;
-    /** Max raw length = MAX_ENCODED_LENGTH * 3 / 4 (~7.5 MB) */
-    private const MAX_RAW_LENGTH = 7864320;
+    /** Max encoded length = 512 * 1024 * 1024 (512 MB) */
+    private const MAX_ENCODED_LENGTH = 536870912;
+    /** Max raw length = MAX_ENCODED_LENGTH * 3 / 4 (~384 MB) */
+    private const MAX_RAW_LENGTH = 402653184;
 
     public function encode(string $data): string
     {