OC 4 - Clicking Confirm Order gives Error 500 when checking out a product with a disabled "required shipping"

As the title suggests I am getting an internal server error on checking out a product with a disabled "required shipping".
I also tested this on a fresh install (no extra extensions), still the same error.
Checkout works only for those products with enabled "required shipping".
I need this to work also for products with disabled "required shipping"
I'm using OC 4.0.2.3.

You need to find your PHP error log (not the OpenCart log) and look to see what the actual error is.