"Thank you for your purchase."message page

Hi,

In most of payment plugin there is a "return url" parameter which is the web page where the user would be redirect after the confirmation of his order.
So you can enter the url of your specific page or article and the user would be redirected to.

Otherwise, you can override the "thank you" page of your payment plugin, you have to copy the file into a specific directory of your template to do it.
But I am quite sure that the payment plugin you use have this "return url" option.

Regards,