I cannot see item on reply from market place listing MacBook Pro

Thanks. In that case please try these suggestions:

If Safari on Mac doesn't open a webpage or isn't working as expected - Apple Support

There are a number of suggestions ranging from the mundane (reload the page) to checking Safari Extensions and other ideas more likely to result in determining what's wrong.

Try restarting your Mac in the usual manner first. It's a simple step that often fixes things.

Edit to add: are you using Facebook Marketplace?

https://www.facebook.com/marketplace/

?

When you do this, are you using Safari on your Mac?

To find out, what appears on the menu at the top of its screen, adjacent to the  (Apple) menu?

Safari looks like this:

More information would help. Describe what you are attempting to do with your Mac, as though we can't see what you're doing.

I'm afraid I still don't understand. You click on an advertisement on your iPhone... then what happens? Someone replies, but how? Email?