The UCD needs to get the customer ID via a different way

Model/AdyenInitiateTerminalApi.php

@@ -27,6 +27,7 @@ namespace Adyen\Payment\Model;
 use Adyen\Payment\Api\AdyenInitiateTerminalApiInterface;
 use Adyen\Payment\Model\Ui\AdyenPosCloudConfigProvider;
 use Adyen\Util\Util;
+use Magento\Quote\Model\Quote;
 
 class AdyenInitiateTerminalApi implements AdyenInitiateTerminalApiInterface
 {
@@ -106,7 +107,6 @@ class AdyenInitiateTerminalApi implements AdyenInitiateTerminalApiInterface
         $serviceID = date("dHis");
         $initiateDate = date("U");
         $timeStamper = date("Y-m-d") . "T" . date("H:i:s+00:00");
-        $customerId = $quote->getCustomerId();
 
         $request = [
             'SaleToPOIRequest' =>
@@ -148,6 +148,8 @@ class AdyenInitiateTerminalApi implements AdyenInitiateTerminalApiInterface
                 ],
         ];
 
+        $customerId = $this->getCustomerId($quote);
+
         // If customer exists add it into the request to store request
         if (!empty($customerId)) {
             $shopperEmail = $quote->getCustomerEmail();
@@ -188,4 +190,13 @@ class AdyenInitiateTerminalApi implements AdyenInitiateTerminalApiInterface
         $quote->save();
         return $response;
     }
+
+    /**
+     * @param Quote $quote
+     * @return mixed
+     */
+    public function getCustomerId(Quote $quote)
+    {
+        return $quote->getCustomerId();
+    }
 }