I have the same problem. They will not send invoices automatically!
Can someone help me URGENT! What should I do?

Once the purchase is complete, appears this: Internal Server Error
The server encountered an internal error or misconfiguration and was unable to complete your request.
Please contact the server administrator, This e-mail address is being protected from spambots. You need JavaScript enabled to view it and inform them of the time the error occurred, and anything you might have done that may have caused the error.
More information about this error may be available in the server error log.
Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.

My domain: www.hvcklimauredjaji.com

Please help!