hi,
First of all;
- I just checked your order history, apparently you have purchased MaterialMart from us
- But you opened a thread in the wrong forum-category
- In your message, you said: I am using CleanMart.
You are all wrong from top to bottom.
You also said: "i use ... one page checkout plugin"
and asking our help with the problem with checkout. "One Page Checkout Plugin" is not our extension, you should ask help from the developer of that plugin.
You can try to re-naming this folder:
/templates/YOUR_TEMPLATE/html/com_virtuemart/cart/
to
/templates/YOUR_TEMPLATE/html/com_virtuemart/cart2/
to completely disable the checkout template-override of MaterialMart. So, "One Page Checkout Plugin" will be 100% responsible to control the checkout pages -- but i don't think this will solve anything, your problem is related to checkout plugin you use, has nothing to do with MaterialMart.
Regards.