Problem with the pre-installed Paypal Express Button in OC 2.3.0.2

I am using Opencart 2.3.0.2. When I enabled the Paypal Express Checkout Button in the module page, the following msg appeared with I ran a test payment:

Notice: Undefined index: PAYMENTREQUEST_0_SHIPTOZIP in /home/XXXXXX.com/catalog/controller/extension/payment/pp_express.php on line 285Warning: Cannot modify header information - headers already sent by (output started at /home/XXXXXX.com/catalog/controller/startup/error.php:34) in /home/XXXXXX.com/system/library/response.php on line 12

This message wouldn't appear if doing the checkout normally instead of clicking on the paypal express checkout button. I am using a clean opencart 2.3.0.2 with no extensions nor amendments made at all. So I believe there is a problem with the existing Paypal Express Checkout Button extension, which is a pre-installed extension included in opencart.

Anyone knows how to fix this?

Check your private messages

The issue was a missing postal code in Paypal address callback information.

I am having the same issue with 2.3.0.2. Have turned Paypal express off until I can get to the bottom of it.