Hello, Dailysoap House!
You probably have a problem with some of the active plugin incompatibility.
Basically, the first thing to try, is to deactivate All currently active plugins, if after that the Vision Core plugin can be activated without the error, live it active and activate the plugins one by one until the problem reoccurs so on that way you will find the problematic plugin (if any).
Please check the following post, to find out where the problem is:
https://theme-vision.com/forums/topic/agama-pro-http-500-error/#post-15728
As I wrote in the previous post without the active “Vision Core” plugin isn’t possible to register the theme.
Please let me know what happens when you try the steps from the link above.
Best Regards