I am trying to buy the plugin but it give me empty message and do not complete the purchase process.
Hi @ali.roshdy,
Thanks for reaching out!
We are sincerely sorry for the problem you encountered on the Bubble checkout page but it would be better to reach the Bubble Support team and ask them why this could happen. Why contact Bubble Support - all our plugin sales are going through the Bubble platform and we cannot influence the payment process in any way as it is related to the Bubble competence. 
Would you kindly contact the Bubble Support team and let us know if they were able to help you: Contact | Bubble
Best regards,
Gulce