I'm making a site for a client using Joomla and I need your help to set up a custom form that gets submitted after a paypal payment has been made. Basically I need to create an article on which I will write some rules for a competition and then, below those, there has to be a form that gets sent after the paypal check out gets done. How can I make this possible?
Forget about creating an Article, install a Form builder extension to create a form that has the field that you require and place the 'rules' in the text before the fields. Use the return URL form Paypal to point to your Form.
Alternatively create a form using a form builder extension and then embed it in an article using a plugin like those available from Regular Labs or any of other similar plugins for embedding modules in articles.
If you are familiar with writing raw PHP code then you can find similar plugins that allow you to embed PHP into your Article.