Customers have been experiencing issues while checking out.

After clicking "confirm order", the screen refresh with a red highlighted message: " Your order has changed. Please check value....and resubmit"

I tried a test order and i am getting the same message. If i try several times, the order eventually goes thru.

Any ideas on how to fix it please? Thank you

Site is royal-fleur.com with squarewebpay

ZC 1.5.7
OPC 2.5.1
PHP 7.4

I enable the debug and I am getting the follow files but they are too long to post on here