Hello,
I hope you're doing well, let me get right into it.
The usual cause of a 500 error is a misconfigured .htaccess file OR its automatic display by your code or CMS.
I know exactly what to check to fix this for you and I can do it right now within 1 hour.
I know what I'm doing and I'm good at it, I've worked on many big projects here on Freelancer and all of my clients gave me great reviews and constructive feedback, feel free to check it on my profile. Allow me to handle this for you once and for all.
Thanks for reading,
Mario Adabachy.