Paypal payment screen and thank you pages not show

The Paypal form and the thank you pages on my site are not showing.
The form was showing at one point, but now it is gone.
Can you give me some common solutions for this problem?
Thank you.

PS.
Your support does not show any solutions and you just ask people to give them your login information.
The installation instructions ( ext4joomla.com/jddoc/ ) are full of spelling mistakes, link errors and are not really complete.
This is very disappointing altogether

Extra information

1. I have setup the forms in Email & Messages: /administrator/index.php?option=com_jdonation&view=configuration
2. I have not setup the paypal redirect message, because I do not know what it's for.
3. After a succesfull payment I am redirected to /index.php?option=com_jdonation&view=complete&Itemid=0 which is an empty page

Hi Gerben,
I have replied your ticket
Thanks
Dam