My site received another log file over the last weekend...

[15-Jul-2022 17:36:43 America/New_York] Request URI: /ajax.php?act=ajaxOnePageCheckout&method=validateCustomerInfo, IP address: 5.81.xxx.xxx (IP from UK)
#1 trigger_error() called at [/public_html/includes/classes/OnePageCheckout.php:1300]
#2 OnePageCheckout->validateAndSaveAjaxCustomerInfo() called at [/public_html/includes/classes/ajax/zcAjaxOnePageCheckout.php:401]
#3 zcAjaxOnePageCheckout->validateCustomerInfo() called at [/public_html/ajax.php:85]
--> PHP Fatal error: validateAndSaveAjaxCustomerInfo, invalid POST: array (
) in /public_html/includes/classes/OnePageCheckout.php on line 1300.

It is an intermittent issue (all other orders over the last weekend are good) and it is my first time to see this error. I did some search in this post and it is recommended to set "Payment-Block Action on Shipping Change" to "update". I set it to "no-update" currently.

I'm using USPS/FedEx and PayPal express & payment pro. So if I'm right, those payment blocks don't need an update. The reason I set it to "no-update" is that I don't want the customer to re-enter the credit card info again if he changes the shipping method, and "no-update" seems working fine for a majority of the cases.

BTW last Friday, I updated my OPC from 2.4.2 beta to 2.4.2.

Please let me know. Thanks in advance.