make payment page a step

No, I don't think so. I tried to figure out exactly how it all works out, but I didn't. I looked around in a decompiler, but couldn't figure out when exactly the cms is clearing the shopping cart and making the order.

My guess is that you need a custom provider, or to customize the DocumentWizardManager web part to do that.

In my case, I didn't need the payment form at all, so I just load it and redirect to my 3rd party payment form.

Hi,

The order creating code is placed in App_Code\CMSModules\Ecommerce\CMSCheckoutWebPart.cs. Method FinalizeCheckout() is called only when we are on the last step and the Next button (Page wizard button webpart with next action) was clicked.

You have to create an order before paying for it. Therefore it is a best practise to place the payment step outside the checkout process. The payment page can look like part of the process, but without back button (Order has been already created).

In case you still want to build the payment form as the last step, you have to modify the CMSCheckoutWebPart and call FinalizeCheckout method before customer reaches payment step and handle back button (or hide it).