Hi,
I'm not clear on the situation.
Is the screenshot linked with PayPal Checkout ?
The screenshot seems to come from the URL of a product details page with its product not available.
But you're talking about a problem with PayPal Checkout, and the URL you provided is the one at the end of the checkout process.
Did you provide the wrong screenshot maybe ?
I also tried to look at your checkout, but I can't access your website from where I am:
i.imgur.com/tfx3hH5.png
In your message, you're saying " 500 error ", but I don't see this at the top of the screenshot. Do you see that it is a 500 error from somewhere else ?
Normally, when you have a 500 error on a page, you need to activate the "debug" setting of the Joomla configuration and reproduce the issue. That way, you get the full error message with the call stack, and this will allow us to understand where the problem is.
Are you able to try this ?