Hello,
I suggest you enter the checkout page a button to remove the coupon posted by customers

Thank you for your suggestion. At present VirtueMart cart helper does not have any separate task to remove a coupon from cart session. VP One Page Checkout uses all core VirtueMart tasks through Ajax calls. If we need to made available your suggestion then we will have to add a new task to core cart helper of VirtueMart. That will be a kind of core hack which we never accept for any of our extensions. However we will look for some other alternative ways and if possible we will include your suggestion in the next updates of the plugin.

Ok, thanks a lot jumbo.
I just wanted to say that I have noticed one thing.
With shopping cart virtuemart gate if I click on the coupon and save the coupon is removed.
As if I do the same thing with the plugin onepage the coupon is not deleted.

This is just to let you know

Thanks for the information.