Hi,
I have read your project and understand that the 500 internal server error might be due to either any resource exceeds like RAM/CPU or any scripts causing the issue. If you can provide the SSH root access to the vps, we can check it and correct it right now.
We are a team of individual server administrators having many years of experience in the field of Linux/Windows administration, Cloud Management Services etc.
Hope to hear from you soon.
Regards,