One-Page Checkout [Support Thread]

[lat9]

I also am getting "Your order's details have changed. Please review the current values and re-submit." it is like loop and I cannot get past it.
Setup:
OPC 1.4.1
zenCart 1.55e
The default "responsive_classic"
Payment: Third party credit card payment
can you help me? thanks.

I can try. What is the name of the third-party CC payment method? If that's the only other checkout-related addition you've made to the site, that's probably the issue.